body odor essay

September 26, 2023

Your Body Odor Could Be Used to Track Your Movements or Health

Human scent signatures could one day be collected at places like crime scenes and COVID testing sites 

By Chantrell Frazier , Kenneth G. Furton , Vidia A. Gokool & The Conversation US

The scent emitted from your hands could offer clues about who you are.

Sjo/Getty Images

The following essay is reprinted with permission from The Conversation , an online publication covering the latest research.

From the aroma of fresh-cut grass to the smell of a loved one, you encounter scents in every part of your life. Not only are you constantly surrounded by odor, you’re also producing it. And it is so distinctive that it can be used to tell you apart from everyone around you.

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Your scent is a complex product influenced by many factors, including your genetics. Researchers believe that a particular group of genes, the  major histocompatibility complex , play a large role in scent production. These genes are involved in the body’s immune response and are believed to influence body odor by encoding the production of specific proteins and chemicals.

But your scent isn’t fixed once your body produces it. As sweat, oils and other secretions make it to the surface of your skin,  microbes break down and transform  these compounds, changing and adding to the odors that make up your scent. This scent medley emanates from your body and settles into the environments around you. And it can be used to track, locate or identify a particular person, as well as distinguish between healthy and unhealthy people.

We are   researchers who   specialize in  studying human scent through the detection and characterization of gaseous chemicals called  volatile organic compounds . These gases can relay an abundance of information for both forensic researchers and health care providers.

Science of body odor

When you are near another person, you can feel their body heat without touching them. You may even be able to smell them without getting very close. The natural warmth of the human body creates a temperature differential with the air around it. You warm up the air nearest to you, while air that’s farther away remains cool, creating  warm currents of air  that surround your body.

Researchers believe that this plume of air helps disperse your scent by pushing the millions of skin cells you shed over the course of a day off your body and into the environment. These skin cells  act as boats or rafts  carrying glandular secretions and your resident microbes – a combination of ingredients that emit your scent – and depositing them in your surroundings.

Your scent is composed of the volatile organic compounds present in the  gases emitted from your skin . These gases are the combination of sweat, oils and trace elements exuded from the glands in your skin. The primary components of your odor depend on internal factors such as your race, ethnicity, biological sex and other traits. Secondary components waver based on factors like stress, diet and illness. And tertiary components from external sources like perfumes and soaps build on top of your distinguishable odor profile.

Identity of scent

With so many factors influencing the scent of any given person, your body odor can be used as an identifying feature.  Scent detection canines  searching for a suspect can look past all the other odors they encounter to follow a scent trail left behind by the person they are pursuing. This practice relies on the assumption that each person’s scent is distinct enough that it can be distinguished from other people’s.

Researchers have been studying the discriminating potential of human scent for over three decades. A 1988 experiment demonstrated that a dog could distinguish  identical twins living apart  and exposed to different environmental conditions by their scent alone. This is a feat that could not be accomplished using DNA evidence, as identical twins share the same genetic code.

The field of human scent analysis has expanded over the years to further study the composition of human scent and how it can be used as a form of forensic evidence. Researchers have seen differences in human odor composition that can be classified based on sex, gender, race and ethnicity. Our research team’s 2017 study of 105 participants found that  specific combinations  of 15 volatile organic compounds collected from people’s hands could distinguish between race and ethnicity with an accuracy of 72% for whites, 82% for East Asians and 67% for Hispanics. Based on a combination of 13 compounds, participants could be distinguished as male or female with an overall 80% accuracy.

Researchers are also producing models to predict the characteristics of a person based on their scent. From a sample pool of 30 women and 30 men, our team built a  machine learning model  that could predict a person’s biological sex with 96% accuracy based on hand odor.

Scent of health

Odor research continues to provide insights into illnesses. Well-known examples of using scent in medical assessments include  seizure and diabetic alert canines . These dogs can give their handlers time to prepare for an impending seizure or notify them when they need to adjust their blood glucose levels.

While these canines often work with a single patient known to have a condition that requires close monitoring, medical detection dogs can also indicate whether someone is ill. For example, researchers have shown that dogs can be trained to  detect cancer  in people. Canines have also been trained to  detect COVID-19 infections  at a 90% accuracy rate.

Similarly, our research team found that a laboratory analysis of  hand odor samples  could discriminate between people who are COVID-19 positive or negative with 75% accuracy.

Forensics of scent

Human scent offers a noninvasive method to collect samples. While direct contact with a surface like touching a doorknob or wearing a sweater provides a clear route for your scent to transfer to that surface, simply standing still will also transfer your odor into the surrounding area.

Although human scent has the potential to be a critical form of forensic evidence, it is still a developing field. Imagine a law enforcement officer collecting a scent sample from a crime scene in hopes that it may match with a suspect.

Further research into human scent analysis can help fill the gaps in our understanding of the individuality of human scent and how to apply this information in forensic and biomedical labs.

This article was originally published on The Conversation . Read the original article .

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Why Do I Have Strong Body Odor?

Causes and how to get rid of strong body odor

• Causes of Strong Body Odor
• Reducing Strong Body Odor
• Medical Treatments

Body odor (BO) is a normal part of being human. Hormones, certain medical conditions, and the food you eat can cause strong body odor or changes in the way that you smell. Strong body odor is often perceived as being unpleasant, but there are ways to prevent or treat BO.  This article discusses the causes of strong body odor, tips for reducing it, and medical treatments for body odor that doesn’t improve with preventative measures.

Verywell / Brianna Gilmartin

What Causes Strong Body Odor?

Sweat itself doesn't have a smell. Body odor comes from the bacteria that live on sweaty parts of your body, like your armpits. When you sweat, these bacteria break down certain proteins in your sweat into acids, causing an odor.

Whether your sweat causes body odor depends on the glands releasing it. You're more likely to have body odor when your sweat comes from apocrine glands, which release sweat from hair follicles found in the armpits, groin, and pubic area. Sweat from these glands, produced when you're hot or stressed, contain fats and other compounds that smell when broken down by bacteria.

Eccrine glands, on the other hand, are found all over your skin and squeeze out sweat through a duct to regulate your body temperature. This sweat lacks the fats and other compounds that can smell when broken down by bacteria.

Additional external factors can also contribute to how you smell.

Weight Changes

When you gain weight, you may develop more skin folds. These folds can hold sweat and bacteria, which create ideal conditions for strong body odor.

Onions, garlic, and some cruciferous vegetables contain sulfur, which can build up and come out through eccrine sweat glands, making body odor even stronger.

Spicy foods can also make you sweat more, which in turn can give you a stronger scent.

Medical Conditions

Some conditions can change your normal body scent. These include diabetes , kidney problems or liver disease, and an overactive thyroid . Some very rare genetic conditions can also change your body's odor.

In some cases, an odd body odor can be a sign of something more serious. For example, a bleach-like or urine-like smell may indicate kidney or liver problems.

Stress increases your heart rate and sends a signal to your sweat glands to begin producing sweat to help regulate your body temperature and balance your body's fluids. While sweat may be released through the eccrine glands, most stress-induced sweat will come out of the apocrine glands, which create smellier sweat.

So, you may notice an increase in body odor right before or during a stressful event.

If your family members have smellier sweat, you may be more likely to have it, too. Genes are one of the factors that determine your individual odor.

Excessive Sweating

A condition called hyperhidrosis can cause you to sweat a lot . People with this condition may sweat even when they don't feel excessively hot or stressed.

Menopause may also cause an increase in sweat due to changes in hormone levels that affect your body's ability to regulate temperature. And some people just naturally sweat more than others.

Hormones (Pregnancy or Puberty)

Shifting hormones during pregnancy can raise your body temperature and can make your body think it's hotter than it actually is. The combination can cause you to sweat more than usual, leading to body odor.

Puberty is another time when people may have more body odor than usual. That's because the surge in hormones makes sweat glands more active, allowing for the kind of sweating that causes BO.

How to Get Rid of Strong Body Odor

Body odor can be embarrassing. Fortunately, in most cases, it doesn't signal a serious problem. There are things you can do to banish body odor, or at least tone it down.

Shower Daily

Shower at least once a day. Use soap or shower gel and lather up thoroughly. Pay special attention to the areas prone to body odor.

If you are in a very hot or humid area, you may need to shower twice a day. You can also use a washcloth to wash just your armpits, groin, and skin folds. Be sure to shower immediately after you exercise or sweat.

Use Anti-Bacterial Soap

If regular showers don't seem to help, try a special cleanser. These include:

• Anti-bacterial soap or body wash like Dial
• Benzoyl peroxide cleanser

These washes can help reduce the amount of bacteria on your skin.

Choose the Right Underarm Products

There are two types of underarm products: deodorants and antiperspirants.

Deodorants make your underarms less hospitable for bacteria. They also help mask body odor with a fragrance. Antiperspirants block sweat glands to reduce perspiration.

If you don't sweat much but still get body odor, deodorants are a good choice. If you sweat a lot, look for a product that is both an antiperspirant and a deodorant.

If you have strong body odor, look for a product with higher amounts of active ingredients. If over-the-counter products don't seem to help, talk to a healthcare provider. You might benefit from a prescription antiperspirant/deodorant .

Wear Breathable Fabrics

Natural fabrics like cotton are better than polyester, nylon, and rayon at controlling body odor. Natural fibers breathe; this lets sweat evaporate.

Avoid fabrics that trap sweat against the skin. These create a better breeding ground for body odor. When working out, choose moisture-wicking fabrics.

Change Your Diet

Remove or reduce spicy or pungent foods from your diet. This includes foods like:

• Spicy peppers
• Brussels sprouts

These foods can cause a more pungent sweat. Even alcohol can change the smell of your sweat.

If you eat these types of foods regularly, try eating less of them or stop eating them altogether. This might help improve your body odor.

Shave or Wax

Apocrine glands are concentrated in areas covered by hair. This includes the armpits and the pubic area.

Hair holds sweat and makes a good home for bacteria. Removing hair can help control body odor.

Consider shaving your underarms. If you'd rather not go bare, try trimming the hair short. This can also help reduce body odor.

Medical Treatments for Body Odor

If you've tried these tips and haven't seen an improvement, call a healthcare provider. Something else may be causing your body odor, such as a fungal infection. Or, you just may need a stronger treatment.

Consider these options:

• Prescription antiperspirants/deodorants are stronger than what you can get over the counter. These are usually the first treatment step for body odor.
• Antibiotics , either topical or oral, can help reduce bacteria on the skin.
• Botox (onabotulinumtoxin A) injections can reduce your sweat glands' ability to produce sweat. This is not a permanent fix, though. Treatment needs to be repeated every few months.
• Laser treatment reduces hair follicles. This may not help with body odor, though.
• Surgery to remove sweat glands can be done in extreme cases.

Body odor is caused by bacteria breaking down the sweat from the apocrine glands in your armpits, groin, and pubic area. 

You may be more prone to body odor if you are overweight, eat certain foods, have certain health conditions, or are under stress. Genetics may also play a role.

You can prevent body odor with lifestyle changes like daily showering and choosing the right underarm product.

If you still have body odor after trying these things, ask a healthcare provider about prescription medication or medical procedures that might help.

Hamada K, Haruyama S, Yamaguchi T, et al. What determines human body odour ? Exp Dermatol. 2014;23(5):316-7. doi:10.1111/exd.12380

Harvard Health Publishing. What's that smell? Get rid of body odor .

International Hyperhidrosis Society. 6 ways to control stress sweat .

Callewaert C, De Maeseneire E, Kerckhof FM, Verliefde A, Van de Wiele T, Boon N. Microbial odor profile of polyester and cotton clothes after a fitness session .  Appl Environ Microbiol . 2014;80(21):6611–6619. doi:10.1128/AEM.01422-14

Chen W, Zhang X, Zhang L, Xu Y. Treatment of axillary bromhidrosis in adolescents by combining electrocauterization with ultrasound-guided botulinum toxin type A injection . J Plast Reconstr Aesthet Surg. 2021;S1748-6815(21)00193-5. doi:10.1016/j.bjps.2021.03.089

Pastor DK, Harper DS. Treating body odor in primary care . Nurse Pract . 2012;13;37(3):15-8. doi:10.1097/01.NPR.0000409913.95393.28

By Angela Palmer Angela Palmer is a licensed esthetician specializing in acne treatment.

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Processing of Body Odor Signals by the Human Brain

Bettina m. pause.

Department of Experimental Psychology, University of Duesseldorf, Universitaetsstraße 1, 40225 Duesseldorf, Germany

Brain development in mammals has been proposed to be promoted by successful adaptations to the social complexity as well as to the social and non-social chemical environment. Therefore, the communication via chemosensory signals might have been and might still be a phylogenetically ancient communication channel transmitting evolutionary significant information. In humans, the neuronal underpinnings of the processing of social chemosignals have been investigated in relation to kin recognition, mate choice, the reproductive state and emotional contagion. These studies reveal that human chemosignals are probably not processed within olfactory brain areas but through neuronal relays responsible for the processing of social information. It is concluded that the processing of human social chemosignals resembles the processing of social signals originating from other modalities, except that human social chemosignals are usually communicated without the allocation of attentional resources, that is below the threshold of consciousness. Deviances in the processing of human social chemosignals might be related to the development and maintenance of mental disorders.

Introduction

« L'odeur d'un corps, c'est ce corps lui-même que nous aspirons par la bouche et le nez, que nous possédons d'un seul coup, comme sa substance la plus secrète et, pour tout dire, sa nature. L'odeur en moi, c'est la fusion du corps de l'autre à mon corps. Mais c'est ce corps désincarné, vaporisé, resté, certes, tout entier lui-même, mais devenu esprit volatil. » (Sartre 1947 , p. 201) 1 .

In his essay about the French lyricist Charles Baudelaire, Sartre literarily describes the process of body odor perception in humans. Even though body odor is made of physically describable matter, it can be regarded as an indicator of the impermanence of being because it is also highly volatile. Hence, the existentialist understands body odor to be a unique composition out of being and nothingness. Therefore, in the view of Sartre, the human body odor symbolizes the true nature of human beings. Accordingly, during the smelling process, the soul and the body of an individual are incorporated by the perceiver. As a result, the perceiver's soul and body merge with the soul and body of the odor sender.

Just recently, the perception of human body odors has been investigated by use of methods of the modern neurosciences. Whereas the question whether body odor resembles the true human nature might remain subject to further philosophical debates; however, the neurosciences may help to answer the question, whether chemicals derived from human body fluids are capable of changing the feelings and cognitions of the perceiver. In the following, it will be discussed whether chemical communication in humans is related to the transmission of information relevant for ontogenetic and phylogenetic survival. Evolutionary theories even point to the possibility that the complexity of the human brain, at least in part, derived from the ability to perceive, process and adapt to social chemosignals of conspecifics.

Social Communication

Social behavior is ubiquitous in the animal kingdom and essential for the survival of diverse mammalian species. Social behavior includes attraction of potential mates, the regulation of social distance, the soothing and restoring of social equilibrium, and the engendering of help from conspecifics. All of these social actions seem to be associated with the experience of basic emotions (Levenson 2003 ) in humans and other mammals (Burgdorf and Panksepp 2006 ; Panksepp 2011 ). Whereas the successful operation of such social actions obviously supports phylogenetic survival, it has recently been stated that social complexity was the main promotor of the primate's brain size (Dunbar 1998 ). A growing number of different studies coherently report that the neocortex in anthropoid primates increases with different indicators of social complexity, e.g., group size, grooming clique size, the frequency of coalitions, and the prevalence of social play (see Dunbar and Shultz 2007a ). While predation risk has been postulated as the ultimate cause for group living (Dunbar and Shultz 2007b ), social enrichment requires the development of behavioral flexibility, which in turn is essential for the formation of stable social bonds. Within the neocortex, the volume of the ventromedial prefrontal area has been considered to be intimately linked to social competencies in humans (Lewis et al. 2011 ). In addition, besides coding the biological significance of stimuli in general (Pessoa and Adolphs 2010 ), the amygdala seems to be the main paleocortical relay for the processing of social information in primates (Emery and Amaral 2000 ; Sallet et al. 2011 ) and humans (Bickart et al. 2011 ).

Social communication is based upon a successful release and processing of different sensory signals, including speech, touch, biological motion, facial expressions, and chemosensory signals. In comparison to the communication via other sensory modalities, social communication through chemosensory signals has several advantages (Wyatt 2003 ). Chemosensory signals can be used in darkness and can easily cross barriers. Depending on the volatility of the molecules, chemosensory signals might be transmitted across very long distances. In contrast, low volatile molecules might still keep the information for conspecifics at the place of release, while the sender has already disappeared (Pause et al. 1997 ). Hereby, solely the communication through chemical signals is proficient to carry information about social events that happened in the past. Furthermore, social chemical signals are usually based on a specific mixture of molecules, while the meaning of the signal not only depends on the molecules within the mixture but also on the concentration of each molecule. Therefore, the number of signals which could carry social information is extremely high.

The processing of and reaction to environmental chemical signals might have been of special importance for the evolution of the vertebrate brain. Even as early as 1904, it was proposed that the telencephalon was originally an olfactory structure invaded by other sensory systems over the course of vertebrate evolution (Edinger 1904 ). In fact, the brains of the jawless fish, the modern representatives of the most primitive vertebrates, lampreys, and hagfish, are dominated by huge olfactory bulbs (Eisthen 1997 ; Northcutt 2002 ). The view that the olfactory system of the jawless fish (lamprey) represents the most ancient version of the vertebrate olfactory system is supported by sequence analyses of the olfactory receptor gene family (Freitag et al. 1999 ). Furthermore, recent high-resolution X-ray computed tomography of fossil mammalian skulls indicates that the special features of the mammalian brain evolved through the improved ability of mammals to analyze and process the complex olfactory environment (Rowe et al. 2011 ). During successive evolutionary pulses, first, the olfactory bulb and olfactory (piriform) cortex expanded. About 200 million years ago, a species which resembles the basal-most member of Mammaliaformes ( Morganucodon ) showed a first major pulse in encephalization, with a brain about 50% larger than that of earlier related mammal-like reptiles. This encephalization was mainly due to the expansion of the olfactory bulbs. A second encephalization pulse was assessed in the closest known fossil relative of living mammals ( Hadrocodium ) and was again associated with a marked increase in brain size, and especially of the olfactory bulbs and the cerebral hemispheres. Finally, the huge olfactory receptor genome developed, which was accompanied by olfactory epithelial growth. It can be concluded from these findings that the ability to optimally adjust to the chemical environment was far more important for the huge encephalization in mammals than the ability to process visual or auditory stimuli.

In summary, evidence is accumulating that during vertebrate and mammalian evolution, the ability to adjust to the chemical complexity of the social and non-social environment was the main or one of the main forces for brain development. In primates, however, social complexity has been considered to be the main promotor of neocortex development. It could be speculated, that social chemical communication in humans is still highly complex and important for phylogenetic survival and successful development. The role of chemical communication in humans might have been strongly underestimated as chemical communication between humans usually does not reach the level of conscious processing. However, it is commonly agreed, that in order to adjust to the environmental social requirements, social signals commonly require a fast and automatic response and are therefore mostly processed implicitly without the allocation of attentional resources (Frith and Frith 2008 ; Öhman and Mineka 2001 ; Tamietto and de Gelder 2010 ). In the long run, the investigation of human chemosensory communication will show how deeply the chemical senses are involved in human communication. In fact, first reports suggest that even highly sophisticated social emotions, like moral disgust, might have their evolutionary origin in the processing of chemical signals (Chapman et al. 2009 ; for a controversial view see Herz 2011 ).

Body Odor Signals

Whereas body odors can derive from different body fluids (urine, vaginal secretions, sperm, tears) the products of the glandular systems in the skin have usually been considered to be valid sources of human body odor (for an exception see Gelstein et al. 2011 ). Out of the three primary gland systems, the sebaceous glands, the eccrine glands and the apocrine glands, the sweat produced by the apocrine glands has received most attention. The apocrine glands are located primarily round the nipples, genitals and the axillary region. They develop fully in puberty and are unique to humans and great apes. Apocrine sweat glands secrete a variety of odor precursors that are transformed into volatile odoriferous substances by bacterial enzymes on the skin surface. The secretion of the aprocrine gland is adrenergic innervated through sympathetic fibers. Therefore, the secretion is related to autonomic activation which in turn is associated with motivational or emotional experiences.

A signal can be defined as a stimulus which carries a message to a receiver. Within social communication, the signal is produced and released by a sender. Thus, in contrast to a pure stimulus, which may or may not carry relevant information, a social signal always conveys specific information between two individuals. Therefore, in understanding human communication, it is necessary to focus on the transmitted information, which can be isolated easiest by analyzing the effect of the communication in the signal receiver. So far, four areas of human chemosensory communication have been studied in more detail, each demonstrating physiological and/ or behavioral consequences of signal perception in the receiver. They are related to kin recognition, mate selection, menstrual cycle synchronicity, and emotional contagion.

Kin recognition is most important for structuring social relations in many diverse species (see Mehdiabadi et al. 2006 ). In order to promote inclusive fitness, which can be understood as the successful transmission of one's own and relatives' genes to the next generation, pro-social behavior is favored among family members (Hamilton, 1964 ). However, unrelated individuals, like out-group members are more easily perceived as aversive (Olsson et al. 2005 ) and more easily attacked (De Dreu et al. 2010 ). Given the importance of kin recognition, numerous studies have shown that newborns are able to chemosensorily identify their mothers, that mothers and fathers are able to chemosensorily identify their children, that siblings recognize each other by smell, and that even unrelated individuals are able to match family members by smell (see Porter 1999 ; Porter and Schaal 2003 ).

Similar to kin recognition, a successful mate selection, which forms the basis for the production of healthy offspring, is also a necessary prerequisite for phylogenetic survival. The major histocompatibility complex (MHC) is a highly polymorphic gene complex. It encodes glycoproteins that deliver peptides to the cell surface during antigen presentation, thereby creating histocompatibility or self identification for the immune system. It has been shown in several species that the individual MHC-type is associated to an individual body odor profile, which can be used to chemosensorily discriminate between conspecifics. Fertile individuals prefer the body odors of partners with a relatively dissimilar MHC type to their own. This preference, in turn, seems to be one of the major reasons for mate selection in many vertebrates (Boehm and Zufall 2006 ; Restrepo et al. 2006 ). It has been proposed that this differential mating helps to maintain the high MHC polymorphism within species. A high MHC polymorphism enables the species members to resist to a broader array of pathogens, which is crucial for survival. In reference to the immunological function of the MHC, in humans, it is called human leukocyte antigen (HLA). Humans seem not only to exert body odor preferences for HLA dissimilar individuals but also to preferentially select partners who possess a relatively different HLA type (Havlicek and Roberts 2009 ; Jacob et al. 2002 ). Thus, HLA-associated body odors seem to be used as signals for mate choice.

Another research field in human chemosensory communication is related to the phenomenon of menstrual synchrony. Some 40 years ago, McClintock found that women living or spending time together show a synchronized menstrual cycle (McClintock 1971 ). About 30 years later, it could be demonstrated that this phenomenon is most probably due to the communication of menstrual cycle related chemosignals (Stern and McClintock 1998 ). Whereas odorless axillary sweat samples of women in the follicular cycle phase shortened the menstrual cycle of the female recipients, chemical signals derived from sweat samples of women in the ovulatory cycle phase lengthened the menstrual cycle phase of the signal receivers. This study was the first to show that not only the behavior, but also the endocrine status in humans is prone to be influenced by human chemosignals. However, the evolutionary significance of synchronized menstrual cycles in women is still debated (Mc Clintock 2002 ; Schank 2001 ).

The most recently discovered area of chemosensory communication in humans is related to the detection of danger and emotional contagion. It is common across the animal kingdom that stressed individuals inform their conspecifics via chemosignals about a potential harm (e.g., a predator attack). Even though the release of the signal is associated with an increased risk for the sender to encounter direct threat, the development of this communication might have been evolutionary successful, because all signal receiving conspecifics benefit from signal perception. In rodents, the release of chemosensory alarm signals is associated with activity of the pituitary-adrenal axis and secretion of adrenocorticotropin (ACTH; Abel 1994 ). Physiological reactions to these signals within the receiver resemble stress-related adaptations (Fanselow 1985 ; Kikusui et al. 2001 ; Moynihan et al., 2000 ). Therefore, it is postulated that the experience of stress can be chemosensorily transmitted from the sender to the receiver.

Across phyla, the perception of such stress-related chemosignals seems to be associated with avoidance of the odor source and immediate withdrawal behavior (von Frisch 1941 ; Mackay-Sim and Laing 1981 ; Müller-Velten 1966 ; Ressler et al. 1968 ; Suh et al. 2004 ; Zalaquett and Thiessen 1991 ). A reliable indicator of the activation of motor systems related to withdrawal behavior is the startle reflex. The startle reflex can be measured in animals (Davis et al. 1993 ) and humans (Lang et al. 1990 ) and is increased during states of negative affect and decreased during states of positive affect. As rats (Inagaki et al. 2008 , 2009 ) and humans (Pause et al. 2009 , Prehn et al. 2006 ) show an augmented startle response in the context of chemical stress signals, it is concluded that motor systems related to signal avoidance are automatically primed through the perception of stress-related chemosignals of conspecifics.

Besides the effects on motor behavior, the perception of stress-related chemosignals significantly alters the perception of visual social signals in humans. In the context of chemosensory stress signals, the perceptual acuity to happy facial expressions is reduced (Pause et al. 2004 ; Zernecke et al. 2011 ), and the perceptual acuity to negative facial expressions is increased (fear: Zhou and Chen 2009 ; anger: Mujica-Parodi et al. 2009 ). Moreover, when presented in the context of chemosensory stress signals, neutral or ambiguous facial expressions attract additional attentional resources (Rubin et al. 2011 ).Thus, chemosignals related to stress or other negative emotional states reliably alter visual social perception: the acuity for social signals related to safety is reduced while at the same time the acuity for social signals related to harm is increased.

In summary, several studies impressively demonstrate that human body odors convey important social signals. These signals deliver information about kinship, immunogenetic mating characteristics, the endocrine status, and emotional states reflecting potential transient danger. In fact, social communication might be one of the most important functions of chemosensory perception in humans (Stevenson 2009 ). It should be added that the behavioral significance of single substances (e.g., androgen steroids) which can be detected in human body fluids is far less obvious. This is not surprising, taking into account that usually mixtures of several compounds, which are active only in a certain concentration range, form the biologically active signal (Wyatt, 2003 ). Therefore, several authors conclude, that in humans, behaviorally relevant properties of single molecules have as yet not been demonstrated (Doty 2010 ; Pause, 2004a , b ; Wyatt 2009 ; Wysocki and Preti 2004 ).

Neuronal Processing of Body Odor Signals

So far, the neuronal processing of body odors has been investigated using the event-related potential (ERP) technique, positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). ERPs are the averaged epochs of the electroencephalogram (EEG) that occur time-locked to the presented stimuli. As long as chemosensory stimuli elicit the ERP, the term chemosensory ERP (CSERP) has been applied. Latency and amplitude of the CSERP components provide information about early, pre-attentive, and late evaluative stimulus processing. The CSERP technique offers a very high temporal resolution, but only a poor spatial resolution. By use of the PET technique, biochemical components of neural transmission can be detected, e.g., the regional glucose uptake. As compared to fMRI, the temporal resolution is much and the spatial resolution slightly lower. The fMRI method provides an indirect measure of neural activity measuring the blood flow. This method has the highest spatial resolution and also a relatively good temporal resolution.

In the investigation of olfaction a number of studies could repeatedly demonstrate the activation of primary (piriform cortex, amygdala, entorhinal cortex) and secondary olfactory brain structures (hippocampus, hypothalamus, thalamus, orbitofrontal cortex, insula) through odors (Sobel et al. 2003 ). While the primary olfactory cortex is composed out of areas receiving direct input from the olfactory bulb, areas of the secondary olfactory cortex are directly connected to brain areas of the primary olfactory cortex.

Processing of HLA-Associated Body Odors

CSERP analyses revealed that body odors of donors with a similar HLA type to the perceiver are processed faster and activate more neuronal resources than body odors of donors with a dissimilar HLA type to the perceiver (Pause et al. 2006 ). Whereas rating studies on body odor preferences (e.g., Wedekind and Füri 1997 ) and studies on mating behavior in humans (e.g. Ober et al. 1997 ) could only report a correlative relationship between the HLA system and the relevant indicators of behavior, this was the first experimental study to demonstrate that the brain preferentially processes information about HLA similarity over information about HLA dissimilarity. The evidence of this study suggested that the behavioral impact of chemosensory signals related to HLA similarity might be stronger than of signals related to HLA dissimilarity. As the HLA loci are the most polymorphic loci in the human genome (Parham & Ohta 1996 ), the probability of meeting unrelated individuals with a dissimilar HLA type is extremely high. Therefore, the development of a preference for potential partners with a dissimilar HLA type might be related to other factors than to chemosensory cues, whereas the rejection of potential partners with a similar or identical HLA type might be most effectively determined by the rarely occurring chemosignals of self. Furthermore, it has been proposed that MHC-regulated inbreeding avoidance might lead to higher fitness benefits than MHC heterozygosity (Penn 2002 ). Accordingly, inbreeding avoidance could be successfully achieved if MHC similarity is transmitted as a signal activating avoidance behavior. Therefore, in humans, HLA-related signals seem to be associated with a negative selection bias in mating behavior.

Processing of Body Odors of Kin and Non-Kin

So far, one PET study investigated whether body odor of kin is processed differently from body odor of non-kin (Lundström et al. 2009 ). Even though the participants could not consciously differentiate between the body odors of their sisters and their friends, the regional cerebral blood flow was higher in the fronto-temporal junction, the insula, and the dorsomedial prefrontal cortex during kin recognition. The activation of the dorsomedial prefrontal cortex is discussed to be related to self-referent stimulus processing during kin recognition (Lundström et al. 2009 ; Lundström and Olsson 2010 ). Thus, this study provides further evidence that genetic similarity is recognized through an automatic self-referential process and is therefore in line with the CSERP result that processing immunogenetic similarity is biologically more relevant than processing immunogenetic dissimilarity (Pause et al. 2006 ). The study further demonstrates, that kin is chemosensorily recognized by the human brain without the allocation of attentional resources. This result is in line with the well known phenomenon that social signals are usually processed implicitly (Frith and Frith 2008 ).

Processing of Body Odors Related to the Reproductive State

Even though the phenomenon of the communication of the reproductive state between women (Stern and McClintock 1998 ) has not been investigated using brain imaging techniques so far, one study investigated indirectly whether an increase in the level of sexual hormones in men can be detected chemosensorily by the female brain (Zhou and Chen 2008 ). Axillary sweat was collected from men while watching video segments showing sexual intercourse between heterosexual couples. As compared to axillary sweat collected during an emotionally neutral situation, the sex related sweat was primarily processed within the orbitofrontal and the fusiform cortex and within the hypothalamus. The authors concluded that the activation of the hypothalamus and the orbitofrontal cortex could be related to the processing of the emotional significance of the stimuli. Activation of the fusiform cortex is often related to the processing of social signals (faces, voices, or body gestures) and could be due to the social nature of the stimuli.

Processing of Body Odors Related to Different Emotional States

Two brain imaging studies and one CSERP study investigated whether and how stress- or anxiety-related sweat is processed by the human brain. Stress-related sweat was obtained from first-time skydivers (Mujica-Parodi et al. 2009 ), and anxiety-related sweat was collected from university students waiting for their final oral examination in order to reach an academic degree (Pause et al. 2010 ; Prehn-Kristensen et al. 2009 ).

The CSERP study showed that the processing of almost odorless chemosensory anxiety signals requires enhanced neuronal energy (P3 amplitude) originating from medial frontal brain areas (Pause et al. 2010 ). This effect was more pronounced in females than in males, which could be due to the fact that females show a processing advantage for social emotional stimuli (Proverbio et al. 2008 ) and in addition for stimuli with a weak perceptional salience (Li et al. 2008 ).

As compared to sweat samples collected in an emotionally neutral sport condition, sweat samples collected in the anxiety condition activate brain areas involved in the processing of social emotional stimuli (fusiform gyrus) and in the regulation of empathic feelings (insula, precuneus, cingulate cortex). In this study, the odors were hardly detectable and could not be differentiated regarding their intensity, pleasantness, unpleasantness, or familiarity. Thus, again, it was shown that the human brain automatically guides physiological adjustments to chemosensory social signals, without being dependent on conscious mediation. It was further concluded that in contrast to other modalities, the physiological adjustments in response to chemosensory anxiety signals seem to be mainly related to an automatic contagion of the feeling. This interpretation is in line with the startle experiments, showing an automatic activation of withdrawal-related motor systems (Pause et al. 2009 ; Prehn et al. 2006 ), as well as with animal data, suggesting a chemosensory transmission of stress from sender to perceiver. Finally, the speculation of Sartre ( 1947 ) on the consequences of body odor perception might be a fruitful basic approach to the investigation of chemical communication in humans because the phenomenon of emotional contagion through human chemosignals could in fact literally be described as an incorporation of the sender's soul and body.

In contrast to the anxiety study, the stress-related sweat was mainly processed within the amygdala (Mujica-Parodi et al. 2009 ). As the odors in this study were perceived as weak with a comparable emotional valence, and could not be consciously distinguished, the authors excluded the possibility that the differences in brain activity were due to odor characteristics. However, extreme physiological and psychological stress is not related to a specific emotion but activates a diverse set of physiological systems related to a mixture of different positive (e.g., surprise, joy) and negative emotions (e.g., disgust, fear). It is therefore reasonable to assume that the perception of stress-related chemosignals does not activate emotion and empathy-specific neuronal networks but only less specific structures which prime non-specific autonomic adjustments.

The studies on the neuronal processing of human body odor reveal that social chemosensory signals are processed in the human brain differently from common odors (Lundström et al. 2008 ). Instead, human social chemosignals seem to be processed in brain areas related to the processing of social information, such as the fusiform cortex (social chemosignals: Prehn-Kristensen et al. 2009 ; Zhou and Chen 2008 ; relay of social signal processing: LaBar et al. 2003 ; Hadjikhani and de Gelder 2003 ), the cingulate cortex (social chemosignals: Lundström et al. 2008 ; Prehn-Kristensen et al. 2009 ; relay of social signal processing: Völlm et al. 2006 ), and the insular cortex (social chemosignals: Lundström et al. 2009 ; Prehn-Kristensen et al. 2009 ; relay of social signal processing: Singer and Lamm 2009 ). Moreover, also activations within the medial prefrontal cortex (Lundström et al. 2009 ) and the amygdala (Mujica-Parodi et al. 2009 ) could be related to the processing of significant social signals (Bechara et al. 2002 ).

In line with the consideration that successful social communication is a prerequisite for the unique development of the mammalian brain (Dunbar 1998 ), a new branch of science evolved in the neuroscience during the last decade, called the social neurosciences (Cacioppo and Berntson 2005 ). Meanwhile, the most intriguing progress generated by this new research area may be related to the finding of specialized neural networks within the human brain, which are responsible for the processing of social information (Adolphs 2010 ). Hereby, it has been demonstrated that the perception of other humans' facial expression is different from the perception of common visual objects (fusiform face area, Kanwisher et al. 1997 ). Moreover, social touch, building the basis for the forming of lasting relationships and bonding, might also be processed as a unique social signal (Dunbar 2010 ; Morrison et al. 2010 ). Finally, social feelings, like empathy, require the processing in specialized neuronal relays, different from common non-social feelings (Singer and Lamm 2009 ).

In comparison with the processing of social signals from other modalities, it would be highly unlikely for human social chemosignals to be processed similar to common odors. In fact, all studies investigating the processing of natural complex human chemosignals found neuronal networks involved, which are specialized for the processing of social rather than olfactory information. It is up to future research to investigate whether the specialized network responsible for the processing of human chemosignals within the central nervous system has a correlate in a specialized receptor system for social chemosignals (Brechbühl et al. 2008 ; Liberles and Buck 2006 ).

In order to understand human communication via chemosignals, several phenomenons are waiting for their exploration, e.g., the question which kind of body fluid most effectively conveys social information. Due to the presence of apocrine glands within the axillary region, which are considered to significantly influence the composition of socially relevant chemosignals (Heckmann et al. 2003 ), commonly axillary sweat has been used as the chemosensory stimulus. However, it is also likely that other human body fluids, like tears, contribute to a successful chemosensory communication between humans (Gelstein et al. 2011 ).

Furthermore, chemosensory communication may include much more evolutionary significant information than those investigated so far by brain imaging studies. For example, chemosensory signals most probably convey information related to the actual health status (Arakawa et al. 2011 ; Havlicek and Lenochova 2006 ). Furthermore, the communication of social emotions is probably not restricted to the communication of stress, but might also include other emotions, like sadness (Gelstein et al. 2011 ) or social competition (Adolph et al. 2010 ).

Finally, the analysis of the conditions responsible for an impaired communication via chemosignals might be of special interest in understanding deviant behavior and deviant mental states in humans. For example, it has been shown that individuals scoring high in social anxiety process human chemosignals differently (Zhou et al. 2011 ) and less effectively (Pause et al. 2009 , 2010 ) than non-anxious controls. Therefore, the knowledge of human chemosensory communication might even improve the knowledge about the development and therapy of mental disorders.

It can be concluded, that human social chemosignals are processed as cues for significant behavioral adaptations which are meaningful in terms of evolutionary consequences. Through the communication of chemosignals, social bonds can be formed and maintained (kin recognition), the health status of the immune system in the population is optimized (MHC-associated chemosignals), and relevant changes in motivational (reproductive behavior) and emotional systems are successfully transmitted between conspecifics. The latter is of special importance whenever information about potential harm has to be spread across conspecifics efficiently, automatically and in a lasting manner.

Acknowledgements

We are grateful to Sabine Schlösser for proof-reading the manuscript.

Open Access

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

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Body Odor Similarity Improves Social Bonding and Instant Connections

Claire Gillespie is a freelance writer specializing in mental health. She’s written for The Washington Post, Vice, Health, Women’s Health, SELF, The Huffington Post, and many more.

Verywell / Ellen Lindner

Key Takeaways

• A recent study found that body odor may lead to "click" friendships, where people feel an instant mutual connection.
• Researchers used a device designed to be an "electronic nose" to find that "click" friends have similar body odor.
• Friendship brings many mental health benefits, including combatting loneliness and providing encouragement and reassurance.

Friendships can develop for a number of reasons—shared interests, like-minded attitudes, and sometimes simply being in the right place at the right time.

Another factor might be a surprising one. According to a recent small study, published in the journal Science Advances , people who had an instant personal connection also shared similar body odors.

"Non-human terrestrial mammals sniff themselves and each other to decide who is friend or foe," says study author Inbal Ravebry, one of the researchers in an olfaction lab at the Weizmann Institute of Science in Israel. "Humans also sniff themselves and each other, but the function of this is unknown."

Since humans seek friends who are similar to themselves, the researchers hypothesized that humans may smell themselves and others to subconsciously estimate body-odor similarity, which in turn may promote friendship. 

How Smell Helps Us "Click"

The study involved 20 friendship pairs who said they instantly "clicked". The researchers found that each person's body odor was closer to their friend's than they would expect to be the case purely by chance.

Each friendship pair followed a regimen well-practised in the field of human body odor research—cutting out foods like onions and garlic (which affect body odor) for a few days, and ditching aftershave and deodorant. They also bathed with an unscented soap provided by the lab and slept in a fresh, clean T-shirt (also provided by the lab). The T-shirts were then returned to the researchers for testing.

Using a device that acted like a nose (an eNose), the researchers assessed the odor-causing volatile compounds coming from each T-shirt, with the help of 25 other volunteers to assess the similarity of the smells.

Amy Morin, LCSW

Friendships are crucial to good mental health. Our friends give us a sense of belonging and help us combat loneliness.

The researchers were interested to find that "click" friends have similar body odor and that it was possible to predict clicking by body odor similarity with 71% accuracy (77% when there was a mutual click and 68% when there wasn't).

"This is important because it implies that we may be more like other terrestrial mammals in this respect than we typically appreciate," Ravebry says.

Theresa L. White , PhD, Professor and Chair in the department of psychology at Le Moyne College, New York, says the study is high quality, although she points out that it doesn’t necessarily apply to other types of same-sex friendships (i.e. non "click" connections), opposite-sex friendships, or romantic relationships. 

And while the eNose machine thought that “click” friends smelled more similarly to each other than they did to other people in the study, the machine and the people seem to be using different aspects of the body odor as the basis of their decisions. 

"So, the machine can do what we do, but it does it in a different way," White says.

What Is Subconscious Smelling?

The study also notes that people subconsciously smell each other.

"When we encounter other people, we use all of the information that we have available to make decisions about others," White explains. "Body odor is one source of information, even if we’re not consciously aware that we’re smelling it."

Theresa L. White, PhD

When we encounter other people, we use all of the information that we have available to make decisions about others. Body odor is one source of information, even if we’re not consciously aware that we’re smelling it.

Each person has a unique personal odor that is influenced by genetics, as well as environmental factors such as the food that they typically eat. "Both aspects influence the way that we think of a person, and we can even use that odor as a cue to a person’s identity," says White, who co-authored a paper showing that first impressions are altered through the environmental odors associated with people.

Evidence from previous studies suggests that people's moods and emotions, including how they can be highly affected by odor.

"It definitely has an effect on our perception of an individual (even if we are not consciously aware of the effect) and can also affect our emotional response as measured on independent judgments of the emotional or compentency states of others," says Pamela Dalton, PhD, MPH, an experimental psychologist and faculty member at Monell Chemical Senses Center .

The bottom line of this evidence is that the people around us are constantly giving their emotional/health body states via low level body volatiles and that many people are able to perceive these sensory signals, Dalton explains. "However, being able to perceive these sensory signals at a less than conscious level means that behavior may change without conscious perception," she adds.

Friendships and Mental Health

Friends play a crucial part in protecting our mental heath and wellbeing. "Friendships are crucial to good mental health. Our friends give us a sense of belonging and help us combat loneliness ," says Amy Morin , LCSW.

Not only can friends help us be happier, they can help us find more meaning in life and support us during our times of need. "Spending time with people who care about us helps us feel better. It can give us reassurance that we can get through tough times because we have people who will be with us," says Morin. "Friends may also encourage our healthy habits and may even help us live longer."

Dalton notes that humans are social animals and require companionship from others.  "Subconscious signals that indicate a person is more similar to our lifestyle than others may be a quick prejudicial way to effect an introduction to a friendship ," she says.

Ravreby I, Snitz K, Sobel N. There is chemistry in social chemistry . Science Advance s. 2022 June. doi: 10.1126/sciadv.abn0154

Hovis, N.L., Sheehe, P.R., White, T.L. Scent of a Woman—Or Man: Odors Influence Person Knowledge . Brain Sciences . 2021 July. doi: 10.3390/brainsci11070955

Kontaris I, East B S, Wilson D A. Behavioral and Neurobiological Convergence of Odor, Mood and Emotion: A Review . Frontiers in Behavioral Neuroscience . 2020 Mar. doi: 10.3389/fnbeh.2020.00035

By Claire Gillespie Claire Gillespie is a freelance writer specializing in mental health. She’s written for The Washington Post, Vice, Health, Women’s Health, SELF, The Huffington Post, and many more. 

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In 1781, Benjamin Franklin wrote an essay about farting

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Share All sharing options for: In 1781, Benjamin Franklin wrote an essay about farting

In 1781, Benjamin Franklin decided to write about a truly important scientific topic: flatulence.

"It is universally well known, that in digesting our common food, there is created or produced in the bowels of human creatures, a great quantity of wind,"  Franklin wrote in an essay variously known as "To the Royal Academy of Farting" or simply " Fart Proudly ." "That the permitting this Air to escape and mix with the Atmosphere, is usually offensive to the Company, from the fetid Smell that accompanies it."

Franklin's reason for taking up the topic of farting? To urge the Royal Academy of Brussels, which had put out a call for scientific papers, to take up the goal of discovering "some Drug wholesome & not disagreable, to be mix’d with our common Food, or Sauces, that shall render the natural Discharges of Wind from our Bodies, not only inoffensive, but agreable as Perfumes."

franklin wanted scientists to figure out how to make farts smell good

In other words, statesman, author, scientist, and inventor Benjamin Franklin wanted scientists to focus on creating a medicine that would make farts smell good.

Of course, the whole essay ( which you can read here ) was somewhat tongue-in-cheek. Franklin — who was living in Paris at the time — was frustrated by the impracticality of most questions taken up by the scientific establishment, so he wrote this essay in response, but didn't actually send it to the Royal Academy. Instead, he sent copies to a few friends, including British chemist Joseph Priestley and philosopher Richard Price .

Franklin's dream is still unrealized: we don't have a medicine that makes farts smell good, though we do have drugs (like Beano) that  cut down on gas production . Research has also found that foods which contain hydrogen sulfide — like beans, onions, cauliflower, Brussels sprouts, broccoli, and dairy — disproportionately contribute to farts smelling bad.

In the essay, after making a few shrewd body-odor-related observations (namely, that asparagus makes urine smell bad , and turpentine makes it smell good ), Franklin asserted that the value of a medicine that makes farts smell good would trump many of science's biggest achievements. "What Comfort can the Vortices of Descartes give to a Man who has Whirlwinds in his Bowels!" he exclaimed.

Finally, he concluded with a few puns — declaring that when it comes to practicality, the discoveries of Aristotle, Newton, Descartes, and others are "scarcely worth a FART-HING."

For more on farting: 9 surprising facts about flatulence you may not know

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• Published: 02 April 2019

Body odors (even when masked) make you more emotional: behavioral and neural insights

• Cinzia Cecchetto   ORCID: orcid.org/0000-0001-9047-9884 1 , 2 , 3 ,
• Elisa Lancini 1 ,
• Domenica Bueti 1 ,
• Raffaella Ida Rumiati 1 , 4 &
• Valentina Parma 1 , 5 , 6  

Scientific Reports volume  9 , Article number:  5489 ( 2019 ) Cite this article

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• Olfactory cortex
• Sensory processing

Morality evolved within specific social contexts that are argued to shape moral choices. In turn, moral choices are hypothesized to be affected by body odors as they powerfully convey socially-relevant information. We thus investigated the neural underpinnings of the possible body odors effect on the participants’ decisions. In an fMRI study we presented to healthy individuals 64 moral dilemmas divided in incongruent (real) and congruent (fake) moral dilemmas, using different types of harm (intentional: instrumental dilemmas, or inadvertent: accidental dilemmas). Participants were required to choose deontological or utilitarian actions under the exposure to a neutral fragrance (masker) or body odors concealed by the same masker (masked body odor). Smelling the masked body odor while processing incongruent (not congruent) dilemmas activates the supramarginal gyrus, consistent with an increase in prosocial attitude. When processing accidental (not instrumental) dilemmas, smelling the masked body odor activates the angular gyrus, an area associated with the processing of people’s presence, supporting the hypothesis that body odors enhance the saliency of the social context in moral scenarios. These results suggest that masked body odors can influence moral choices by increasing the emotional experience during the decision process, and further explain how sensory unconscious biases affect human behavior.

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Introduction

Moral choices are most often explained as a result of emotional and cognitive processes 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . However, morality is primarily a social phenomenon, tightly dependent on the social context. In their Relationship Regulation theory (RR), Rai and Fiske 9 highlight the role of social context in shaping moral choices and posit that people are led by moral motives to evaluate and guide one’s own and others’ judgments and behaviors, according to moral rules developed within specific social relationships. In other words, people build a particular moral motive allowing to live in a specific social context while moral transgressions are defined as the circumvention of such specific relational prescriptions 9 . Recent empirical evidence supports this theory: for instance, participants’ moral acceptability of tradeoff scenarios can be affected by unconscious biases, such as intergroup prejudices and stereotypes, and the perception of different social groups influences the neural systems implicated in moral choices 10 .

Unconscious biases can influence moral decisions based on a variety of stimuli such as attitudes (such as dispositions towards people or places) 11 , implicit stereotypes (such as judging a person as attractive or unintelligent because is a cheerleader) 11 or somatic reactions (such as endocrine release or psychophysical reactions) 12 . However, this line of research has not yet considered the possibility of evaluating the effects of social information transmitted via sensory subliminal cues, such as odors. Humans transfer socially-relevant information, such as age, gender, health status, sexual availability and personal predispositions, via body (or social) odors 13 , 14 . Furthermore, odors – including people’s odors – are everywhere and we do not necessarily realize their presence consciously 14 , 15 .

The idea of using olfactory stimuli to investigate moral choices is not entirely new. Landy & Goodwin 16 argued how olfactory influences on morality are greater than those mediated by vision, the sense humans mostly rely on. Additionally, Schnall et al . 17 demonstrated that the presence of a disgusting odor toughens the judgment on vignettes without moral content. Also, as we have previously shown, the subliminal exposure to a neutral odor can bias moral choices towards options characterized by harm avoidance (deontological options) 18 . Generally speaking, a harm is justified, and to some extent forgiven, if it comes as the side-effect of a moral action carrying a greater benefit compared to an intentional harm with the same outcome 19 , 20 . All in all, odors are able to transfer social information and their effect on moral choices seems to modulate harm avoidance.

To our knowledge, previous studies have only explored the behavioral effects of olfactory contextual stimuli on moral choices 17 , 18 . However, whether and how the social context might impact moral decision making when induced via sensory subliminal stimulation, and the neural underpinnings of moral choices under the exposure of masked body odors, are still unknown. A meta-analysis showed that, in absence of odor stimulation, moral (vs. non-moral) choices were found to be associated with increased activations in primarily cognition-related areas (i.e., MTG, left and right middle temporal gyrus; rMFG, right middle frontal gyrus; rIFG, right inferior frontal gyrus) and primarily emotion-related areas (i.e., cingulate gyrus, left precuneus) 21 . However, the way in which moral dilemmas are formulated modulates the competition between the fast, automatic emotional response and the slow, deliberative cognitive system. As previously shown, instrumental dilemmas (Footbridge-type dilemmas) 22 recruit emotion-related brain areas such as medial prefrontal cortex, posterior cingulate cortex/precuneus, amygdala, and brain areas involved in “theory of mind” such as the temporoparietal junction (TPJ) and angular gyrus 1 , 2 , 4 . On the other hand, accidental dilemmas (trolley-type dilemmas) are associated with activations in neural areas involved in working memory and cognitive control, such as the dorsolateral prefrontal cortex and inferior parietal lobe 1 , 2 , 4 .

While the impact of the exposure to body odors on the neural underpinnings of moral choices still remains unexplored, we are now aware that processing body vs. common odors 23 rely on distinct neural pathways, in line with what occurs when social information is presented through other sensory modalities (e.g., Schupp et al . 24 for vision and Belin et al . 25 for audition). Processing body odors recruits the occipital cortex, active when either visual stimuli or socially-relevant stimuli are cross-modally presented 26 , the angular gyrus, responsive to human body related information 27 but also involved in social cognition and multisensory integration; and the anterior and posterior cingulate cortex, previously found implicated in emotion regulation 28 , 29 and self-reflective processes 30 . What still remains to be clarified is whether these regions are also involved in the perception of human body odors during a concurrent cognitively demanding task (such as making moral decisions). If this were the case, we would expect a reduction in the activation of OFC or of the higher order areas described (e.g., posterior cingulate cortex) as a result of a reduced attention for sensory analysis, in line with the reduced activation of amygdala 31 or piriform cortex 32 , 33 observed when complex judgments are performed during odor perception.

In the present work, we hereby tested whether and how introducing a social context through masked body odors impact the behavioral and the neural correlates of moral choices. The aims of the study were the following: (1) to test whether subliminally presented body odors have a selective effect on incongruent moral dilemmas (real dilemmas) or generalize to different types of decision-making scenarios (congruent or fake dilemmas); and (2) to investigate whether and how body odors impact harm avoidance decisions. In the present functional magnetic resonance imaging (fMRI) study, participants were asked to answer to 64 moral dilemmas during the presentation of a fragrance neutral in pleasantness (masker) or to a body odor concealed by the same fragrance (masked body odor). The main dependent variable was the type of moral choice made, which could be utilitarian , if participants decided to execute harmful actions in order to save people, or deontological , if participants decided not to cause harm to not violate societal norms, even if the harm is meant for a greater good 2 , 19 . To explore whether the effect of the masked body odor is modulated by the dilemmatic nature of the presented scenario, half of the dilemmas were congruent, meaning that cognitive and emotional processes converged towards the same deontological action so that they were fake dilemmas, and half were incongruent dilemmas in which the two processes diverged, so they were real dilemmas 34 . Moreover, to clarify the modulation of the type of harm, half of the dilemmas were instrumental (dilemmas in which the harm is deliberate) and the other half were accidental (dilemmas in which the harm is a side effect).

We hypothesized that the presence of body odor would induce the participants to perceive the people involved in the scenario as more concrete, real. If that were the case, then participants are expected to be more prone to follow societal norms not to harm people. We anticipated this effect to be stronger than the increase of deontological answers shown when a neutral odor is presented 18 . Since it has been shown that when dealing with incongruent (compared to congruent) dilemmas, individuals were found to be more willing to provide utilitarian answers 34 , we expected such trend to be reduced in the presence of the masked body odor. Moreover, as in a previous study 18 we observed that the presence of a neutral odor increases the number of deontological answers specifically for instrumental dilemmas, here we expected the presence of the masked body odor to result in an increment of deontological answers for such dilemmas.

With respect to the neural underpinnings, we hypothesized that the processing of incongruent (compared to the congruent) dilemmas would be associated with brain regions commonly implicated in this type of task, such as the amygdala, the ventro-medial prefrontal cortex (vmPFC 1 , 35 , the temporo-parietal junction 36 and the precuneus 21 . Additionally, we predict that the presence of the body odor would favor activations in areas commonly associated with social information, including body odor processing, such as the angular gyrus, occipital cortex, and the anterior and posterior cingulate cortex 14 , 23 . We further hypothesized that when processing dilemmas that describe intentional harm, emotional brain areas, such as the cingulate gyrus or precuneus, would be more strongly activated. We expected that these emotional areas would be more strongly activated in the presence of the masked body odor, even when processing accidental dilemmas, usually associated with cognitive neural areas. However, given the innovative nature of this research, we had no clear predictions as to the specific neural areas to be recruited, and we therefore explore whole-brain activations with respect to this contrast.

Materials and Methods

Ten healthy, heterosexual males donated their body odors in two different days (age: 26.3 ± 3.6 years old (mean ± SD); range = 20–31). Male donors were chosen based on the greater intensity of their body odor axillary secretions 37 . The donors reported: (i) to be non-smokers 38 ; (ii) not to have health issues or to undergo drug treatment known to be related to olfactory alterations; (iii) to have an age ranging from 18 to 35 years old. Informed written consent was obtained from each donor. Each donor agreed to follow behavioral, nutritional (i.e., no alcohol, smoking, food altering the natural body odor) and hygiene instructions throughout the collection session (adapted from) 14 . The medium of body odor collection was a t-shirt, previously washed with an odorless detergent (Liquid Detergent ECOR with no Perfume and essential oils, ECOR 27094). T-shirts were worn by donors for 12 consecutive hours during the day, right after having taken a shower using fragrance-free body wash and having dried themselves with towels washed with the same odor-free detergent used to pre-wash the t-shirts. Donors collected their body odors on separate t-shirts for each day of collection for a total of two days. Odorless plastic bags were provided to each donor to store each of their t-shirts before bringing them to the lab, the day after each collection period 23 , 39 . Samples were perceptually evaluated for odor contamination (e.g., alcohol, smoke, fragrance, food) and for body odor detectability by one to three trained experimenters. All samples were then stored in a −80 °C freezer to prevent sample deterioration 40 .

Participants

The original group of participants was composed of 30 women. The rationale for testing only women is based on the evidence that women show a greater preference for social emotional stimuli 41 , also when presented in olfactory form 42 . The participants followed the same criteria as the donors, and additionally, they had to score at the 16-item Sniffin’ Sticks Identification subtest of the Sniffin’ Sticks Extended test above 10 43 as well as presenting a regular menstrual cycle 44 .

No depression or heightened sensitivity to disgust (Disgust Scale) 45 was revealed. Two participants were removed from the study because of possible clinical problems. The final sample included 28 healthy, heterosexual, right-handed women aged between 19 and 34 (23.7 ± 4.2 years), who were normosmic (TDI score: 13.4 ± 1.5, range = 11–16), and whose STAI state score before the task was within the normal range (STAI state score: 33.7 ± 4.3, range = 24–42). Participants were instructed to not eat or drink anything but water one hour prior to testing, and to not wear any scented products on the day of testing. The SISSA Ethics Committee approved the study, which is in accordance with the Declaration of Helsinki and an informed written consent was obtained from each participant.

General procedure

At the beginning of the experiment, participants were seated in a quiet room and they were instructed about the experiment. Then participants performed the odor identification test 43 and they completed the State questionnaire of the State-Trait Anxiety Inventory (STAI-S) 46 . Anxiety state data were collected because previous literature has shown that moral choices are modulated by individual variability in anxiety 18 , 47 , 48 . To test whether the masking procedure supposed to cover the body odor produced the expected perceptual impact to the same extent across olfactory conditions, participants were asked to rate intensity, pleasantness and familiarity of the masker, masked body odor and clean air before and after the moral decision-making task. The three tasks were all performed inside the scanner in order to override the possible confounding effects of the MRI scanner setting. The procedure of the odor-rating task and of the moral decision-making task was similar to the one applied in previous study 18 (see Supplemental Information for details about the two tasks). Then, outside the scanner, participants completed again the STAI State questionnaire 44 . See Fig.  1 for an overview of the experimental procedure.

Overview of the experimental procedure. ( A ) Overview of the experiment session; ( B ) Overview of a single trial of the moral decision-making task. See Fig.  S1 of the Supplementary Information for an overview of the type of moral dilemmas and odor conditions.

Odor stimuli

Two odor conditions were presented within participants. One set of dilemma alternatives (N = 32) was presented during the exposure to an emotionally neutral, rather unfamiliar odor (aka, masker odor ; 200 μL of cedarwood oil, Sigma-Aldrich), as determined via pilot studies (see Supplementary Information of 49 for detailed descriptions of the odor pilots) and as confirmed by previous study 18 . The masker odor was applied to equally-sized quadrants of cotton white t-shirt previously washed with the same detergent used for the t-shirts worn by the donors. The second set of dilemmas alternatives (N = 32) was presented during the exposure to the masked body odor . The masked body odor was prepared by including in a glass jar four donated t-shirt quadrants (supradonor) chosen from all those collected from the 10 donors and one clean t-shirt quadrant on which we applied 200 μL of masker odor 50 . The masking procedure was used to simulate the hygiene products usually used with the goal of making the paradigm more ecologically valid 51 . As customary in human body odor research 14 , 52 , 53 , 54 , 55 , each recipient smelled one supradonor stimulus across all dilemma trials, but in order to reduce the stimuli similarity 52 , the combination varied in terms of the axilla the sample came from and the day at which it was collected. The order of the two odor conditions presentations was randomized across subjects and across the four blocks of the moral decision-making task.

Odors were presented bi-rhinally in a temporally-precise, square-shaped manner using a computer-automated olfactometer 56 . A low bi-rhinal flow rate of 1.0 L/m (a total of 0.5 L/m per nostril) was used to prevent irritation of the nasal mucosa over time 56 , 57 . Odor stimuli were delivered directly to both participants’ nostrils from a nasal manifold, attached to the participant’s chest by means of a chest strap, connected to the olfactometer via Teflon tubing.

Odor rating task

A green fixation cross lasting for 0.5 s preceded each odor presentation. The odor presentation lasted for 4.0 s and was accompanied by a black screen. Subsequently, a white screen was presented for 6.0 ± 0.1 s (mean ± SD) during which participants were asked in succession and in a random order to answer the following questions: “How intense was the odor you just smelled?”, “How pleasant was the odor you just smelled?”, and “How familiar was the odor you just smelled?”. During question presentation, clean air was released to minimize odor residuals 56 . Perceptual ratings for odor intensity, pleasantness, and familiarity were collected on a 10-cm computerized Visual Analogue Scale (VAS), ranging from “not at all” to “very much”. Participants were instructed to answer even if they did not perceive any odor. The odor rating task was performed inside the scanner to reduce the time of the experimental session, but without collecting functional MRI data.

Moral decision-making task

The 4CONFiDE moral set described in Cecchetto et al . 20 was reshaped for this study to include congruent and incongruent dilemmas. A total of 64 dilemmas was presented, 32 congruent and 32 incongruent. Furthermore, half of the congruent and incongruent dilemmas were accidental and the remaining instrumental. Each dilemma type was presented in 16 alternative versions to allow for the presentation of the same factor combination in both odor conditions. The order of presentation of the dilemmas was randomized across participants to exclude any presentation order effects on moral decision-making (see Fig.  S1 in the Supplementary Information for a visualization of the features of the dilemma set).

Each dilemma was presented on two subsequent screens. The first screen described the scenario, in which a danger threatens to kill a group of persons, and a hypothetical action would save these people but cause the death of another person. The second screen presented the question Do you…[action verb] so that…? Participants had to choose between four options: “I certainly do it”, “I do it”, “I do not do it”, and “I certainly do not do it”. The first two choices are held to be utilitarian, as they maximize overall utility (i.e., saving more lives), whereas the latter two were non-utilitarian (deontological).

Before starting the moral decision-making task, participants performed two practice trials. An Italian version of the instructions suggested by Christensen et al . 19 and previously used in Cecchetto et al . 20 was administered.

See Fig.  1 for an overview of the moral decision-making task. Each trial began with a black cross that was displayed for 5.0 ± 0.3 s. Then, a green cross was presented for 1.2 ± 0.2 s and the odor delivery started. Subsequently, the scenario was presented for 22.0 s. The scenario presentation was combined with the odor presentation. Afterwards, the question slide was presented together with the releasing of clean air to minimize odor residuals 56 . The four choices were displayed below the question. Participants had maximum 5.0 s to answer. After the answer a black cross was presented for 5.0 s.

The 64 dilemmas were divided into four blocks that corresponded to four scanning runs. During each block, 16 trials balanced for moral dilemmas types and odor conditions, were presented in randomized order. Participants were allowed to take a short break at the end of each run while lying in the scanner. Dilemmas were presented using a black font color (font: Calibri, size: 24) against a white background. Stimulus presentation was delivered with E-prime 2.0 software (Psychology Software Tools, Pittsburgh, PA).

Behavioral data analysis

Frequency analysis was performed on the four response options to see whether the number of each option changed based on the odor condition. Since no significant differences were found among the four response options in relation to odour condition, we collapsed them for the subsequent analyses.

Behavioral data were analyzed with linear mixed-effects models (LMMs) 58 using R (version 2.10.1; http://www.r-project.org/ ) and in particular using the lme function ( nlme package; https://cran.r-project.org/web/packages/nlme/nlme.pdf ) for continuous variables and the glmer function ( lme4 package; http://cran.r-project.org/web/packages/lme4/index.html ) for binary variables (deontological or utilitarian answer). To account for individual differences (e.g., some people are more “deontological” than others), participants were included in the models as random factors. To avoid a warning of non-convergence, an optimizer (bobyqa) was applied 59 . Results with and without the optimizer are not significantly different ( https://github.com/lme4/lme4/blob/master/misc/notes/release_notes.md ). Estimates on the choice between utilitarian and deontological responses were based on an adaptive Gaussian Hermite approximation of the likelihood with 10 integration points. For odor ratings, models with odor and session were tested. For moral choice, two models were performed: the first included odor, as the main variable of interest of our analysis, and congruency. The second model included odor and intentionality and it was performed considering only incongruent dilemmas.

Outliers in reaction times were determined by means of the outliers-labelling rule 60 . From a sample of 1792, 127 trials were removed for no response (N = 127/1792, 7.08%), and 43 trials were removed because of extremely long choice reaction times (>2.6 s; N = 43/1665, 2.58%; mean of reaction times is 820.8 ± 507.2 s). Conditions have equivalent final samples of trials (Masker odor = 810, Masked Body odor = 812; X 2 1  = 0.0025, p = 0.96).

MRI data acquisition and pre-processing

A 3 Tesla Philips Achieva whole-body MR Scanner at the University Hospital of Udine (ASUI Udine, Italy), equipped with an 8-channel head coil, was used for MRI scanning. Head movement was minimized through cushioning within the coil. Functional volumes were obtained using a whole-head T2 * -weighted echoplanar image (EPI) sequence (repetition time [TR] = 2.5 s, echo time = 35 ms, flip angle = 90°, 28 transverse axial slices with interleaved acquisition, 3.50 × 3.59 × 4.00 mm 3 voxel resolution, field of view = 230 × 230 mm 2 , acquisition matrix = 68 × 62, SENSE factors: 2 in the anterior–posterior direction). The number of volumes acquired varied for each participant and run given the task duration based on participants’ reaction times (mean number of volumes per run = 260 ± 4.6, range = 153–270). Anatomical images were acquired during the final odor rating task as 180 T1-weighted images (0.75 mm slice thickness). Stimuli were viewed through VisuaStim Goggles system (Resonance Technology) mounted to the head coil, which was adjusted on each participant’s vision. Responses were made and recorded through one MR-compatible response pads (Lumitouch, Lightwave Medical Industries, Coldswitch technologies, Richmond, CA) using the right hand. To minimize influences of breathing effects, participants were instructed and trained to maintain a constant and normal breathing rate. Due to technical problems, images from the first session of one participant and the second session of another participant were removed from the analysis.

Data were analyzed with SPM12 (Wellcome Trust Centre for Neuroimaging, London, UK). All functional volumes were spatially realigned to the first volume, slice- time corrected, segmented in gray matter, white matter and cerebrospinal fluid tissues, spatially normalized to the standard EPI template, and smoothed using a Gaussian kernel with full width at half maximum (FWHM) of 8 mm 3 . Movement-related variance was analyzed using the Art toolbox ( www.nitrc.org/projects/artifact_detect ). For each run, outlier scans were identified based on the TR-to-TR composite motion more than 2 mm and/or considering whether the scan-to-scan global BOLD signal normalized to z-scores deviated from mean more than z = 3. The time-points identified as outliers were regressed out as separate nuisance covariates in the first-level design matrix. All participants displayed a percentage of outlier scan inferior to the cutoff (25%), therefore no one was excluded from the analyses and all trials were retained.

fMRI data analysis

Two separated fMRI data analyses were carried out: in the first analysis, odor conditions and congruency of dilemmas were considered to explore whether the effect of masked body odor was modulated by the dilemmatic nature of the presented scenario; in the second analysis, which was performed only on incongruent dilemmas, odor conditions and intentionality as the type of dilemmas were considered to investigate the effects of masker body odor on the processing of different types of harm.

Statistical analyses were performed using a general linear model (GLM) approach. In the first-level analysis, data were analyzed separately for each participant. In each trial, four events were modelled: the presentation of clean air, of an odor, of the scenario combined with an odor and, of the slide including the question. The duration of each of these events was set to 0 except for the scenario presentation, which was set to a fixed time of 22.0 s. The combination of these four event types with dilemma congruency (congruent vs incongruent) or dilemma intentionality (accidental vs instrumental) and the two odor conditions (masker vs masked body odor) led to a total of 16 regressors for each run. The six motion parameters were also included as regressors of no interest in the design matrix. All regressors were convolved with a canonical hemodynamic response function. Low-frequency signal drifts were filtered using a cutoff period of 128.0 s. As a next step, at the individual level, contrast parameters were estimated for all the 16 regressors of interest, averaged across the four runs. Subsequently, at the second-level analysis, 4 contrast images of the event scenario presentations from the combination odor with congruency or intentionality of each participant were submitted to a flexible factorial design, with subject as random factor, odor conditions and congruency or intentionality as fixed factors, to assess neural activations of the dilemma processing during the exposure to the odor. Later, the 4 contrast images were entered to linear contrasts of the repeated measure ANOVA with two within-subject factors to investigate main effects and interactions. To identify the neuronal substrates of single odor condition or single dilemma type, simple main effects (i.e., [masker odor – masked body odor] for each odor condition and each dilemma type separately) were analyzed. To investigate whether odor conditions affect neural activity related to moral dilemma processing, we performed a dilemma type (i.e. congruent/incongruent or accidental/instrumental) by odor condition (masker odor/masked body odor) interaction at group level. Moreover, to clarify whether the neural underpinnings involved in the masker body odor effects for one dilemma type (i.e. incongruent or accidental) are shared by the opposing dilemma type (i.e. congruent or instrumental), exclusive and inclusive conjunction analyses were performed between the neural areas recruited for the interactions [odor × congruency or intentionality].

Finally, in order to investigate the relationship between brain activations and moral choices, the mean beta values of the activated clusters were extracted using the REX toolbox (Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, MA) and simple correlation analyses were performed with the percentage of utilitarian responses.

Whole-brain analyses were thresholded at p < 0.05, family-wise error (FWE) cluster-level corrected for multiple comparisons across the whole brain. The AAL2 toolbox 61 , 62 was used to guide the labelling of the activated clusters.

Masked body odor and masker are perceptually similar

We first tested whether the masking procedure applied to cover the masked body odor had the expected perceptual impact and rendered the olfactory conditions equivalent in their basic perceptual dimensions. The LMM on intensity ratings (clean air: 2.45 ± 0.13 points; masker: 5.83 ± 0.18 points; masked body odor: 6.10 ± 0.16 points; see Fig.  2A and Table  1 ) revealed that both the masker and the masked body odor were perceived as significantly more intense than clean air ( p  < 0.001; reference factor: clean air), but no significant difference was found between the masker and the masked body odor ( p  = 0.48; reference factor: masker). A difference emerged when looking at the effect of session (pre moral decision-making task: 5.23 ± 0.21 points; post moral decision-making task: 4.56 ± 0.20 points; p  = 0.024): odors were rated as less intense during the second session compared to the first session suggesting that participants might have adapted during the task (Dalton, 2000).

Distribution of participants’ odor ratings. The black dots represent single data points, whereas the box-plot represents the interquartile range of each distribution, with the thick black horizontal bar corresponding to the median. Each box-plot is surrounded by a violin plot representing the smoothed distribution of data. Significant differences (p < 0.05) are indicated with a star.

The LMM on familiarity ratings (clean air: 3.78 ± 0.14 points; masker: 5.61 ± 0.20 points; masked body odor: 5.91 ± 0.17 points; see Fig.  2B and Table  1 ) showed that both the masker and the masked body odor were perceived as significantly more familiar than clean air ( p  < 0.001; reference factor: clean air), but no significant difference was found between the masker and the masked body odor ( p  = 0.40; reference factor: masker). No significant differences were found between the ratings performed before and after the task ( p  = 0.32; reference factor: pre).

The LMM on pleasantness ratings (clean air: 4.48 ± 0.12 points; masker: 4.89 ± 0.16 points; masked body odor: 4.58 ± 0.18 points; Fig.  2C ) showed no significant differences across the three odor conditions. Moreover, no significant differences were found between sessions. Please, refer to Table  1 for descriptive data.

State anxiety is increased at the end of the task

A Wilcoxon test (W = 148801, p  < 0.0001) determined that participants’ state anxiety was increased at the end of the task (34.36 ± 6.45 points, range = 22–48) as compared to its beginning (33.67 ± 4.33 points, range = 24–42; see Fig.  S2 in the Supplementary Information).

Irrespective of odor condition, incongruent dilemmas produce more utilitarian responses

First, the model including odor conditions, congruency and the interaction between them was performed (see Table  2 for descriptive data of single parameters). There was a significant effect of congruency on moral choice: the likelihood of choosing the utilitarian option increased when dilemmas were incongruent (z = 10.08, p  < 0.001). In other words, when cognitive and emotional processes diverge (real dilemmas), more utilitarian answers are produced than when cognitive and emotional processes converge (fake dilemmas). No significant effects were found for the main effect of odor condition or for the interaction odor × congruency.

Irrespective of odor condition, accidental dilemmas produce more utilitarian responses

Considering the results of the previous model, we tested the effect of odor conditions, intentionality and the interaction between these two factors on incongruent dilemmas only (see Table  3 for descriptive data of single parameters). A significant effect of intentionality emerged (z = −0.43, p  < 0.001): in incongruent dilemmas, the likelihood of choosing the utilitarian option increased when dilemmas were accidental (vs instrumental). The odor condition, alone or in interaction, did not affect the type of moral choice made.

fMRI brain activations

Areas involved in moral cognition are selectively activated by incongruent dilemmas.

The processing of real dilemmas (contrast incongruent vs congruent dilemmas) revealed activations in the left middle frontal gyrus, left inferior parietal gyrus and bilateral precuneus (see Table  4 and Fig.  3A ). The correlation analysis performed between beta values and percentage of utilitarian answers did not show significant results. No significant activations emerged when considering the processing of fake dilemmas (congruent vs incongruent dilemmas).

Brain activation maps showing significant cluster of activations for ( A ) Incongruent >Congruent: significant activations in the left middle frontal gyrus, left inferior parietal gyrus and bilateral precuneus; ( B ) Masked body odor >Masker: significant activations in the left supramarginal gyrus; ( C ) Incongruent (masked body odor >masker) >Congruent (masked body odor >masker): significant activations in the left supramarginal gyrus. Statistical maps are derived with a threshold of p  < 0.05 FWE corrected and superimposed on a standard T1 template. Color scale represents t statistics. Image labels: L = left, R = right.

Activation in visual areas tracks the utilitarian responses to incongruent dilemmas when exposed to the masker odor only

The presence of the masked body odor (vs the masker odor) during the presentation of both incongruent and congruent dilemmas was accompanied by activations in the left supramarginal gyrus (see Table  4 and Fig.  3B ). In contrast, the presence of the masker odor (vs the masked body odor) activates the bilateral calcarine cortex, the left middle occipital gyrus, the right precuneus, the left lingual gyrus and the left posterior cingulum (see Table  4 ). The beta values extracted from the cluster including the bilateral calcarine cortex and the left middle occipital gyrus significantly correlate with the number of utilitarian responses to incongruent dilemmas when exposed to the masker odor ( r  = 0.48, p  = 0.009). No other significant correlation between behavioral responses and neural activations emerged.

The masked body odor during incongruent dilemmas is associated with activations in the left supramarginal gyrus

To identify whether the brain regions that are active components in the masked body odor effect for the incongruent dilemmas are shared also for the masked body odor effect in congruent dilemmas, exclusion and inclusion conjunction analyses were performed between the areas recruited for the interaction “masked body odor and incongruent dilemmas” and for the interaction “masked body odor and congruent dilemmas”. The exclusion conjunction analysis for [incongruent (masked body odor >masker) >congruent dilemmas (masked body odor >masker)] showed that the left supramarginal gyrus was significantly recruited only when the masked body odor was presented during the processing of incongruent dilemmas (see Table  4 and Fig.  3C ). No significant correlations were found between the extracted beta values and percentage of utilitarian answers in this contrast. The inclusion conjunction analysis and the opposite exclusion conjunction analysis did not reveal any significant results.

Emotional areas are involved in instrumental vs accidental incongruent dilemmas

To evaluate the effect of intentionality, only incongruent dilemmas were considered. Processing accidental (vs instrumental) dilemmas significantly activated the left lingual gyrus, left fusiform gyrus, the left inferior occipital gyrus and the left middle occipital gyrus (see Table  5 and Fig.  4A ), whereas processing instrumental (vs accidental dilemmas) was related to significant activation in the bilateral precuneus (see Table  5 and Fig.  4B ). No significant correlations with behavioral responses were retrieved.

Brain activation maps showing significant cluster of activations for ( A ) Accidental >Instrumental: significant activations in the left lingual gyrus, left fusiform gyrus, the left inferior occipital gyrus and the left middle occipital gyrus; ( B ) Instrumental >Accidental: significant activations in the bilateral precuneus; ( C ) Accidental (masked body odor >masker) >Instrumental (masked body odor >masker; significant): significant activations in the left superior and inferior parietal gyrus and in the right angular gyrus. Statistical maps are derived with a threshold of p  < 0.05 FWE corrected and superimposed on a standard T1 template (Coronal and sagittal views are displayed). Color scale represents t statistics. Image labels: L = left, R = right.

The masked body odor during accidental dilemmas is associated with activations in the left parietal and right angular gyri

To clarify whether the brain regions that are active components in the masked body odor effect for the accidental dilemmas are shared also for the masked body odor effect in instrumental dilemmas, conjunction analyses were performed between the neural areas recruited for the interaction “masked body odor and accidental dilemmas” and for the interaction “masked body odor and instrumental dilemmas”. The exclusive conjunction analysis for accidental (masked body odor >masker) >instrumental (masked body odor >masker) showed significant activations in the left superior and inferior parietal gyrus and in the right angular gyrus. The inclusive conjunction analysis and the opposite exclusion conjunction analysis did not reveal any significant results suggesting that the masked body odor modulated only the processing of accidental dilemmas (see Table  5 and Fig.  4C ). The correlation analysis between the beta values extracted and the percentage of utilitarian responses did not reveal any significant results.

Previous research suggests that moral rules are developed within specific social-relational contexts that, in turn, play a critical role in shaping moral choices 9 , 10 . As human body odors are powerful messengers for socially-relevant information 63 , able to modulate the behavior and neural processing of the receiver 13 , 14 , 23 , 39 , 53 , 54 , 55 , we hypothesized that body odors might affect moral choices through the modulation of the perceived social context (i.e., by inducing the perception of the real presence of a person). With this in mind, we asked participants to decide their course of action to moral scenarios while exposed to a neutral fragrance (masker) or to a body odor hidden by the same masker odor (masked body odor). The analysis of the neural correlates revealed that the exposure to the masked body odor: a) modulates the activity in the brain areas involved in the processing of incongruent (real) dilemmas, but not in those involved in the processing of congruent (fake) dilemmas; and b) increases the activations in areas processing sensory and emotional information when incongruent accidental dilemmas are presented.

In our study, we investigated whether masked body odors influence any decision-making task or whether the influence is specific to moral dilemmas, as we had anticipated. The analysis we performed revealed that the masked body odors moderate the neural responses only related to incongruent (but not congruent) dilemmas, increasing the involvement of the left supramarginal gyrus. While presented with a real (incongruent) moral dilemma, the participants immediately experience a negative emotional reaction at the thought of provoking harm: the final decision will be deontological providing that this emotional reaction is sufficiently influential, and that participants have limited time and cognitive resources to make their decision. On the other hand, if participants have enough time, motivation and cognitive resources, they will have the possibility to engage in cognitive deliberation about costs and benefits, in which case the emotional response may be overshadowed, resulting in an utilitarian response to the dilemma 2 , 34 . The information of the masked body odor might interfere with this conflict enhancing the neural pathways that promote prosocial behavior 64 , therefore emphasizing the emotional processing of the sensory information, and facilitate the emergence of deontological responses. This multisensory integration of the social and sensory information provided by the masked body odor, and the emotional information provided by the moral dilemmas involve the left supramarginal gyrus, close to the angular gyrus 1 , one of the neural areas previously found to be associated with the processing of body odors 2 , 3 . The supramarginal gyrus has been often considered as part of the temporo-parietal junction (TPJ) - a neural area typically associated with self-awareness and body-related information processing 4 , 5 and, as such, often involved in tasks of theory of mind 5 , 6 , empathy for pain 7 and in the perception of anxiety body odors 8 . Importantly, these aspects become relevant when considering a body odor in the context of moral dilemmas. Indeed, the centrality of the left supramarginal gyrus in multisensory integration processes has recently been supported in a study that identifies this brain area as an important node for the olfactory-visual processing 9 .

Since in the fake (congruent) dilemmas there is no conflict between emotional and cognitive aspects of the decision (i.e., the benefits do not balance the costs), the social information about the presence of a person becomes irrelevant for the decision itself.

Moreover, in the present study, we clarified whether the masked body odor effect is modulated by the type of harm, being it deliberate (instrumental dilemmas) or an inadvertent effect (accidental dilemmas). Previous studies showed that the accidental harm is judged as being more morally acceptable, it receives higher percentage of utilitarian answers, and it engages lower emotional reactions compared to intentional harming 4 , 64 . Our results are in line with this literature: instrumental dilemmas presented higher percentage of deontological answers and recruited neural areas involved in emotional processing (e.g., precuneus) when compared to accidental dilemmas. Interestingly, the masked body odor seems to moderate the processing of the accidental dilemmas by enhancing the activation of the angular gyrus, which is usually associated with social cognition, multisensory integration and “theory of mind” 27 , and the inferior parietal gyrus, which is important for self-other discrimination 65 . This result seems to support our hypothesis that the presence of a body odor can induce the participant to perceive the social context of the dilemmas as more concrete, as if the odor signaled the presence of a real person, and not just of a hypothetical context. The reason why the masked body odor seems to selectively affect the processing of the accidental and not of the instrumental dilemmas may be due to the higher emotional involvement of the instrumental dilemmas, which prevents the participants to consider the additional emotional information provided by the odor.

The present fMRI data replicate and extend previous findings concerning the neural networks recruited by social odor processing 14 , 15 , 23 . Besides replicating the enrollment of the left supramarginal gyrus, as discussed above, we also showed major activity in the left hemisphere areas. This result, in line with previous studies 23 , 66 , supports the hypothesis that olfactory-mediated affective processes are lateralized in the left hemisphere 67 .

In our study, the body odor was masked by a neutral odor. This masker was applied to simulate the hygiene products usually used to cover the natural body odors we produce and to make the paradigm more ecologically valid 51 . Additionally, it allowed studying the effects of the body odor when they are unconsciously perceived. As seen in previous work 18 , odor effects can emerge irrespective of perceiving the presence of an odor; moreover, masking the body odor limited the inter-individual differences in odor intensity and pleasantness. Such differences can significantly affect decisions, as it seemed in the previous cases when intensity and pleasantness differences across odor conditions were evident 17 , 18 . Here we succeeded in making these conditions perceptually similar for intensity, pleasantness and familiarity, removing the possible confounding effect of these factors on the differences in the moral decisions.

To our knowledge, this is the first study that tests the effects of masked body odors on the neural underpinning of moral decision-making. The present study has some limitations for which future studies are necessary. First, it was designed around a moral decision-making paradigm based on the presentation of moral dilemmas, which felt dilemmatic as the participants’ anxiety levels raised at the end of the task. The use of this sort of dilemmas has been previously criticized (e.g.) 55 , 64 , 68 : (i) dilemmas are described in lengthily written texts, which increase the time needed by the participants to process each stimulus; (ii) to make dilemmas credible they cannot be repeated; (iii) the conceptual factors cannot be analyzed separately, but have to be intermingled in each dilemma. These aspects reduce the possibility to present large numbers of trials, therefore limiting the power of the study. To overcome these issues, we have used here a standardized, culturally-equivalent moral set, specifically designed for imaging experiments, that shows high consistency across the different dilemmas 20 . Moreover, to increase the power of our observations, we based the investigation on a theoretically-motivated interest for one conceptual factor (Intentionality). Despite these efforts, the behavioral analysis failed to reveal any significant mean effects of the odor conditions or significant interactions with odor and dilemma congruency or intentionality. One proposed explanation is that the dilemmas were designed to simultaneously assess also other conceptual factors, such as personal force, benefit recipient and evitability. It is for future studies to clarify whether the masked body odor elicits different effects on moral choices when different conceptual factors are considered (see for example) 69 . Second, the participants’ respiratory patterns were not recorded and incorporated in the fMRI data processing. Although this is common practice in many olfactory neuroimaging studies 70 , 71 , we invite future studies to investigate whether the breathing patterns to human body odor can have an impact on the moral decisions made. Third, only one common odor (cedarwood oil) has been used as masker, and the results cannot be generalizable to all common odors. Fourth, future studies should also increase the sample size to allow the comparison of masked body odors effects in women and men and evaluate potential sex-related effects. Lastly, it would be interesting if future investigations would be extended to clinical populations with a deficit in emotion processing, such as patients with lesions in the ventromedial prefrontal cortex 72 , or non-clinical populations with emotional deficiencies, such as those with a lack of empathy or with high levels of alexithymia 73 , 74 , to examine whether the masked body odor effects on moral decision-making can overcome the usual tendency in this population to give higher percentage of utilitarian answers 74 .

To conclude, the value of these results is highlighted by the consideration that most of the moral decisions, from everyday choices to choices that we are forced to make under unexpected circumstances, are made in the presence of other people. Starting from the theory proposed by Rai and Fiske 9 , which advanced the hypothesis that actions and outcomes should be considered in the context of specific social relationships, indeed any action - including violence and impure acts - can be perceived as morally acceptable depending on the social relationships it takes place in 9 , body odors were used as a means for triggering the social context and for making the social norms more salient. Our results indicate that body odors could effectively mediate moral decisions, possibly increasing the emotional experience during the decision process, and this effect is possible even when the perceiver cannot appreciate the presence of the body odors. Moreover, the current results suggest that, as Cikara et al . 10 posited, the context in which the decisions are made is relevant for understanding which decision is made.

Data Availability

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We would like to thank Luigi Alberto Gozzi for his help in the body odors collection, Carlotta Cogoni and Michele Furlan for their input regarding the neuroimaging analysis. Financial support has been provided by the European Research Council -ERC (Grant Agreement No 682117 BiT-ERC-2015-CoG) to D.B.

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C.C., V.P. and R.I.R. developed the study concept and the study design; C.C., V.P. and E.L. collected the data; C.C., V.P. and D.B. conceptualized data analyses; C.C. performed data analyses under the supervision of D.B. and V.P., C.C and V.P. interpreted the data and drafted the manuscript. E.L., D.B., R.I.R. provided critical revisions. All authors approved the final version of manuscript submission.

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Cecchetto, C., Lancini, E., Bueti, D. et al. Body odors (even when masked) make you more emotional: behavioral and neural insights. Sci Rep 9 , 5489 (2019). https://doi.org/10.1038/s41598-019-41937-0

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How to Write the Body of an Essay | Drafting & Redrafting

Published on November 5, 2014 by Shane Bryson . Revised on July 23, 2023 by Shona McCombes.

The body is the longest part of an essay . This is where you lead the reader through your ideas, elaborating arguments and evidence for your thesis . The body is always divided into paragraphs .

You can work through the body in three main stages:

• Create an  outline of what you want to say and in what order.
• Write a first draft to get your main ideas down on paper.
• Write a second draft to clarify your arguments and make sure everything fits together.

This article gives you some practical tips for how to approach each stage.

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Start with an outline, write the first draft, write the second draft, other interesting articles.

Before you start, make a rough outline that sketches out the main points you want to make and the order you’ll make them in. This can help you remember how each part of the essay should relate to the other parts.

However, remember that  the outline isn’t set in stone – don’t be afraid to change the organization if necessary. Work on an essay’s structure begins before you start writing, but it continues as you write, and goes on even after you’ve finished writing the first draft.

While you’re writing a certain section, if you come up with an idea for something elsewhere in the essay, take a few moments to add to your outline or make notes on your organizational plans.

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Your goals in the first draft are to turn your rough ideas into workable arguments, add detail to those arguments, and get a sense of what the final product will actually look like.

Write strong body paragraphs

Start wherever you want

Many writers do not begin writing at the introduction , or even the early body paragraphs. Start writing your essay where it seems most natural for you to do so.

Some writers might prefer to start with the easiest section to write, while others prefer to get the most difficult section out of the way first. Think about what material you need to clarify for yourself, and consider beginning there.

Tackle one idea at a time

Each paragraph should aim to focus on one central idea, giving evidence, explanation, and arguments that relate to that idea.

At the start of each paragraph, write a topic sentence that expresses the main point. Then elaborate and expand on the topic sentence in the rest of the paragraph.

When you’ve said everything you have to say about the idea, move onto a new paragraph.

Keep your argument flexible

You may realize as you write that some of your ideas don’t work as well as you thought they would. Don’t give up on them too easily, but be prepared to change or abandon sections if you realize they don’t make sense.

You’ll probably also come up with new ideas that you’d not yet thought of when writing the outline. Note these ideas down and incorporate them into the essay if there’s a logical place for them.

If you’re stuck on one section, move on to another part of the essay and come back to it later.

Don’t delete content

If you begin to dislike a certain section or even the whole essay, don’t scrap it in fit of rage!

If something really isn’t working, you can paste it into a separate document, but keep what you have, even if you don’t plan on using it. You may find that it contains or inspires new ideas that you can use later.

Note your sources

Students often make work for themselves by forgetting to keep track of sources when writing drafts.

You can save yourself a lot of time later and ensure you avoid plagiarism by noting down the name, year, and page number every time you quote or paraphrase from a source.

You can also use a citation generator to save a list of your sources and copy-and-paste citations when you need them.

Avoid perfectionism

When you’re writing a first draft, it’s important not to get slowed down by small details. Get your ideas down on paper now and perfect them later. If you’re unsatisfied with a word, sentence, or argument, flag it in the draft and revisit it later.

When you finish the first draft, you will know which sections and paragraphs work and which might need to be changed. It doesn’t make sense to spend time polishing something you might later cut out or revise.

Working on the second draft means assessing what you’ve got and rewriting it when necessary. You’ll likely end up cutting some parts of the essay and adding new ones.

Check your ideas against your thesis

Everything you write should be driven by your thesis . Looking at each piece of information or argumentation, ask yourself:

• Does the reader need to know this in order to understand or accept my thesis?
• Does this give evidence for my thesis?
• Does this explain the reasoning behind my thesis?
• Does this show something about the consequences or importance of my thesis?

If you can’t answer yes to any of these questions, reconsider whether it’s relevant enough to include.

If your essay has gone in a different direction than you originally planned, you might have to rework your thesis statement to more accurately reflect the argument you’ve made.

Watch out for weak points

Be critical of your arguments, and identify any potential weak points:

• Unjustified assumptions: Can you be confident that your reader shares or will accept your assumptions, or do they need to be spelled out?
• Lack of evidence:  Do you make claims without backing them up?
• Logical inconsistencies:  Do any of your points contradict each other?
• Uncertainty: Are there points where you’re unsure about your own claims or where you don’t sound confident in what you’re saying?

Fixing these issues might require some more research to clarify your position and give convincing evidence for it.

Check the organization

When you’re happy with all the main parts of your essay, take another look at the overall shape of it. You want to make sure that everything proceeds in a logical order without unnecessary repetition.

Try listing only the topic sentence of each paragraph and reading them in order. Are any of the topic sentences too similar? Each paragraph should discuss something different; if two paragraphs are about the same topic, they must approach it in different ways, and these differences should be made clear in the topic sentences.

Does the order of information make sense? Looking at only topic sentences lets you see at a glance the route your paper takes from start to finish, allowing you to spot organizational errors more easily.

Draw clear connections between your ideas

Finally, you should assess how your ideas fit together both within and between paragraphs. The connections might be clear to you, but you need to make sure they’ll also be clear to your reader.

Within each paragraph, does each sentence follow logically from the one before it? If not, you might need to add new sentences to make the connections clear. Try using transition words to clarify what you want to say.

Between one paragraph and the next, is it clear how your points relate to one another? If you are moving onto an entirely new topic, consider starting the paragraph with a transition sentence that moves from the previous topic and shows how it relates to the new one.

If you want to know more about AI tools , college essays , or fallacies make sure to check out some of our other articles with explanations and examples or go directly to our tools!

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A Body Odor Essay

As you know from my previous post , I am now living in India. I have been here for about 2 weeks now and, although I already have many stories to tell, I’ll start with one that stinks!  

Yes, this is a post about body odor!

While I was working in Dubai, I have many times heard comments on how Indians smell. In fact, I have heard the expression “little onion” referering to an Indian person, or even just brown people in general. Could have been Bangladeshi, Pakistani… who knows! Although they hate if people mix them up, the truth is that the world tends to put them all under the same category. Some might even say “the curry eaters”. In Dubai, I did come across and worked with several Indians that did in fact have an attention attracting body odor, but I always thought that with the tremendous heat they used to endure, they would naturally sweat and, of consequently, smell. I mean, those laborers who carry materials all day long under 45C weather are not going to smell like roses by the end of the day, are they?!

Who smells good working 12 hours a day under the sun?! NO ONE does!

Putting brown people aside for a moment, let’s focus on black people. When I first told Ashray in Portuguese we have a world to describe the smell of black people he immediately thought we’re damn racists. I guess the colonial past doesn’t help this argument either…. Anyway, the case is that we say black people smell of “catinga”. Catinga basically stands for the strong body odor of a black person.

Why do black people smell?

And what about us whites?! Don’t we smell?! I decided to research this and came across some interesting posts on the internet that suggested white people smell like “wet dog”! And apparently we do smell more than East Asians too!

So apparently white people smell of wet dog or, even better, dead animals!

It’s not the first time I think about body odor and about how it is socially perceived – don’t judge me! We all have our hobbies and interests and turns out smells and poop stories are some of mine!

After a couple of days in India, stripping myself of my Miami Ink t-shirt I felt an Indian scent in the air. My nose naturally went on a research mission and approached the fabric that corresponds to the area underneath my arm pit. And it turns out Miami Ink smelt like curry!!! Do I stink?! I’m not sure if I could call it a stench as such, but it was definitely not my usual body odor. Yes, the one that smells of red carnations, as I am Portuguese after all.

Curry is all around us!…

I had been eating exclusively Indian food for a couple of days in a row and the new diet did affect my smell. It was not one of those “I can’t stay inside a lift with you” sort of smells, but there was definitely a light scent of curried Zara attached to my t-shirt. I have been dating an Indian man for years and he has never smelt like that – why was I smelling of curry?! Was I becoming brown already?!

Spices come in… and spices must come out!

One can only conclude that smells are a very subjective thing. I have read that some races are more prone to body odor than others, as the sweating glands do act differently for different races. But one thing is to sweat (in whatever proportion you might sweat) and another thing would be for your sweat to smell of one specific thing or another, more or less strongly. My own spontaneous research proves that your smell would depend greatly on your food intake.

There's a logical explanation behind most things in life…

Here I am, with this white face like Casper,

Smelling like a stereotypical indian person would.

About a week has elapsed since I first smelt some masala on me. Although I did smell differently for a couple of days, my odor is back to normal now – yes, my green field full of flowers blossoming under the sun scent is back! I have been eating Indian food ever since but I guess my body must have regulated itself somehow and there is no particularly Indian scent no more – believe me, I have more than my nose to attest for this!

And what’s the point of this ramble about sweat

And stinks, you might be thinking.

Well, I meant to open up your mind (and nose) for the fact that anyone can smell at any given point of time  - even if they bathe and use good smelling products! We’re not discussing the cases that happen due to lack of bathing, ’cause if we were to dig into lack of hygiene in this post, that’d be a whole different story. Perhaps we might all smell more than we think and different people can actually feel it even if we don’t. We might be desensitized for the smell of others around us being from our same race or with same eating habits as us and find other people do smell, when maybe amongst themselves they don’t actually find that same smell to be unpleasant.

So smell based racism is not justified (not that any other type of racism is, by the way) and should be frowned upon.

She probably smells like wet dog anyway…

Also, I take the opportunity to share with you that Dove deo for sensitive skin does not do its best job in India – you need something more hardcore!

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10 comments.

This article is actually reminding me of my stay in China. Chinese didn’t care about their body and hygiene at all so they smelled a lot. I was pretty hard or nearly impossible to find a deodorant there.

I had no idea it’d be so difficult to find deodorant in China!!

As an Indian man looking for a nice non-smelling women, where do I go? Looks like that’s the reason I am single. They either stink of body odour or deo mixed with body odour. And why the hell do they get offended when gifted a room freshener? I might have casually mentioned that it can be used as deo as well. So what? Anyway I am done living here. Thinking about moving to China. Apparently, concept of deo is non-existant there. I could fool a local Chinese woman into believing a room freshener to be a deo. She would be the love of my life. I would call her Jasmine. What do you say?

If you decide to go to China in search for eternal love, I’d love to hear your stories!.. ;)

This blog made me laugh, not only because I agree but also because is written in such a light view… i have always thought that we exude what we eat. So it does not surprise me that your shirt smell like curry… but I think that we all smell. the problem is that we get used to our own “scent”. I get that your boyfriend does not smell I have dated a Bangladeshi and I he did not smell. his body odor is different from my usual Mexican friends but it did not stink or smell like curry/masala.. i guess like you i only have issues with people that smell because of lack or hygiene. other than that.. I’m cool By the way I really like you blog.. so I’m definitely going to start following you

Thanks Gopxi!

That’s exactly what I meant: smells because of environment, eating habits and the likes… all good! Whenever it has to do with lack of hygiene… nah, nooo good!! :)

Welcome on board! :)

Que dia tão bom!Descobrir este espacinho.. Enquanto me movimentava pela Escócia, ouvi um comentário em relação ao cheiro dos portugueses, dizem que tresandámos a refogado!hehehehe YEah, refogado smell!!

Obrigada Ines!! :) Refogado?? Nunca tal tinha ouvido! Tao ou mais apetitoso que caril!! :D hahaa..

Our apartment definitely used to smell very Indian because of all the Indian food I made. There is no way to avoid smelling like spices if you make Indian food, but it’s delicious. And I am not Indian :)

Body hodor is also related to DNA. I havent use deodorant in my life cause I don’t produce any body odor, and no one believes me when I say I dont use it at all. As far as I know, most asians don’t have body odor, like japanese. I have read how hard is to find deodorant there, and to be honest, I never felt any smell that I dislike, and I am really complicated with those things. I temp to choose people by how the smell actually, and so far, if I have to point any “race” that i consider have a natural body odor that I cant be around, are actually white people.

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Describing Smells in Writing: Mastering the Art of Sensory Language

By: Author Paul Jenkins

Posted on September 6, 2023

Categories Writing , Creative Writing

The art of describing smells in writing can elevate your work to an immersive experience for readers. The human sense of smell is closely linked to memory, making it a powerful tool for writers to evoke emotions and transport readers into the world they’ve created.

Capturing the essence of a scent in words can be challenging, but with a robust vocabulary and practiced skill, it’s a technique that greatly enhances storytelling.

Understanding the science of smell allows writers to appreciate how scents can influence our perception, emotions, and memories. Developing a robust vocabulary for scents, categorizing them, and accurately describing their intensity will enable writers to paint vivid, olfactory pictures for their readers.

Through practice, observation, and dedication to mastering this art, you will be able to create stories with rich sensory experiences that leave a lasting impact on your readers.

Key Takeaways

• Describing smells effectively in writing can create deeper, immersive experiences for readers.
• Developing a strong vocabulary and understanding the science of smell helps writers enhance their storytelling.
• Practice, observation, and a focus on accurately capturing sensory details lead to richer, more evocative writing.

The Science of Smell

The role of smell receptors.

Your sense of smell relies on specialized receptors in your nose. These receptors detect and identify various types of odor molecules present in the air you breathe. When these molecules reach your smell receptors, they send signals to your brain, which then interprets the scent. There are approximately 10 main categories of scent, such as fragrant, woody, fruity, and chemical.

Sense of Smell and Emotion

Smell has a unique relationship with emotion. Unlike other senses, the olfactory system is closely linked to the brain’s limbic system, which is responsible for processing emotions and memories. This connection essentially means that smells can evoke strong emotional responses, both positive and negative. For example, the scent of freshly baked cookies may bring feelings of comfort and nostalgia, while the odor of rotten food may trigger disgust or repulsion.

Smell and Memory

One of the most impactful aspects of smell is its connection to memory. The relationship between your sense of smell and memory is powerful due to the proximity of the olfactory system to the brain’s hippocampus and amygdala, which are vital for forming and storing memories. As a result, specific scents can bring back vivid memories, even ones that have been seemingly forgotten for a long time.

When incorporating smells into your writing, consider how they might connect with emotions and memories to create a more immersive reading experience for your audience. By effectively describing a variety of scents and the emotions they evoke, you’ll be better equipped to engage your readers and help them establish a strong connection with your narrative.

A Vocabulary for Scents

Adjectives to describe smells.

The world is filled with an incredible variety of scents, and to accurately describe them in your writing, it’s essential to have a diverse vocabulary at your disposal. By using specific adjectives, you can evoke the sensations and memories associated with different smells. Here are some categories of adjectives that will help you describe various scents:

• Fresh : crisp, clean, natural
• Earthy : loamy, musty, damp
• Floral : flowery, feminine, fragrant
• Fruity : citrusy, berry-like, zesty
• Woody : pine, resinous, bark
• Masculine : musky, leathery, smoky
• Chemical : acrid, pungent, rancid
• Sweet : honeyed, sugary, syrupy

These are just a few examples to get you started. Be creative and explore the vast array of adjectives available to you when describing smells in your writing.

Describing Smells through Associations

Another effective way to describe smells in your writing is through associations. Since our sense of smell is closely tied to memory, connecting a scent to a particular experience or situation can create a vivid and relatable description for your reader. By incorporating associations, you will make your descriptions more engaging and authentic.

For example, instead of simply stating that a room smells old, you could describe the scents of dusty, yellowed pages and mothballs, evoking the feeling of a long-forgotten library. Likewise, instead of stating that a bakery smells delicious, you could describe the aroma of warm, freshly-baked bread and buttery croissants wafting through the air.

When using associations to describe scents, consider the following tips:

• Draw upon personal experiences : Reflect on your own memories and emotions that certain scents evoke, and use them to enhance your descriptions.
• Utilize common or relatable experiences : Describe smells that your readers can easily recognize, enabling them to recall similar situations they’ve encountered in their own lives.
• Be specific and detailed : Provide rich and nuanced descriptions of smells, painting a vivid sensory picture for your reader.

Remember, the aim is to create a strong and evocative connection between your description and the scent you’re trying to convey. Experiment with different associations and adjectives to find the perfect way to capture a smell in your writing.

Categories of Smells

Natural scents.

When describing smells, think about the different categories of natural scents that you might encounter in the environment. For example, the scent of flowers can range from sweet and floral such as roses, to more earthy and green as in a pine forest. Fruity smells, like those of lemons or other fruits, often have a fresh and invigorating quality. Earthy smells are common in nature and can evoke a sense of being grounded in the environment. Use these natural scents in your writing to create vivid and authentic descriptions of your settings.

• Floral : rose, jasmine, lavender
• Fruity : lemon, apple, mango
• Green : pine, grass, eucalyptus
• Earthy : damp soil, rain, moss

Man-Made Smells

Man-made smells are those that originate from human activities or created products, such as perfume or sweat. Think about the characteristics of these scents and how they can add layers to your descriptions. Chemical smells can be harsh, pungent, or even nauseating, while perfume scents often bring sophistication or luxury. Describing the smell of sweat can help to convey an atmosphere of physical exertion, labor, or stress. Incorporate these man-made smells in your writing to enhance your storytelling or underscore certain emotions.

• Chemical : bleach, gasoline, ammonia
• Perfume : floral, musky, subtle
• Sweat : salty, metallic, pungent

Complex Scents

Complex scents are a blend of various smells that are often difficult to separate into distinct components. These scents can add depth and interest to your writing, as they are not easily identifiable or may evoke different experiences for different people. When capturing complex scents, consider the layers of smells present, such as a combination of fruity and floral notes or the merging of earthy and green scents. Describing complex scents in your writing can help create a sense of atmosphere and intrigue.

• Fruity floral : a blend of fruit and flower aromas
• Earthy-green : an intermingling of soils and plants
• Lemony-chemical : a mixture of citrus and synthetic elements

Remember to use a confident, knowledgeable, clear, and neutral tone when describing the various categories of smells in your writing. By using second person point of view (you, your, yours), your readers will feel more engaged and connected to the sensory experiences you are conveying.

Describing Intensity of Smells

Light and faint scents.

When describing light and faint scents in your writing, you can draw attention to the subtle nature of the aroma. These scents might require a character to take a deep breath to fully detect them, or they may be barely noticeable. Feel free to use words like delicate , mild , or soft to convey the lightness of a scent. For example, you can describe a gentle floral aroma wafting through the air on a spring day.

Heavy and Strong Scents

Heavy and strong scents are more distinct and tend to linger in the air or on objects. To describe these scents, choose words that evoke their intensity, like robust , rich , or even heady . Your character might walk into a room and immediately notice a heavy, smoky smell hanging in the air. Additionally, you can highlight the warmth associated with certain strong scents, like a spicy or hot aroma, to further convey their potency.

Overpowering Scents

Overpowering scents can be so intense that they dominate the senses and might even cause physical discomfort. When describing these powerful aromas, words like pungent , overwhelming , and intense can effectively convey their force. For instance, your character may feel their eyes watering and nose burning due to an overpowering scent of cleaning chemicals. Pay attention to the characters’ reactions to such smells to emphasize their impact on the scene.

Tips for Describing Smells in Writing

Relating smells to other senses.

When describing smells in your writing, try to relate them to other senses, like taste or touch. By doing this, you can create additional sensory connections for your reader. For example, you could mention that a certain smell is reminiscent of a particular taste or feeling, which can make it easier for the reader to imagine and relate to the described smell. Think about how smells often have similar attributes to tastes, like sweetness or sourness, and incorporate these into your descriptions.

Using Smells to Evoke Emotions

A powerful way to use smells in writing is by connecting them to emotions. As the sense of smell is closely linked to memory and feelings, associating a specific smell with a character’s emotions can effectively convey their state of mind and create an emotional bond with the reader. Consider how certain scents might evoke feelings of happiness, nostalgia, or even fear, and use that connection to enhance the emotional depth of your writing. For example, the smell of freshly baked bread might evoke feelings of warmth and comfort, while the smell of a damp basement might evoke feelings of unease or anxiety.

Choosing the Right Words

When describing smells, it’s essential to choose the right words to convey the message clearly. Be specific and avoid using vague or overly complex language. Instead, use concrete and descriptive terms that will paint a clear picture for the reader. Some helpful ways to do this include:

• Use adjectives : Employ a variety of adjectives to describe the smell’s qualities, such as sweet, pungent, or musty.
• Analogies and metaphors : Draw comparisons between the smell and other recognizable scents, tastes, or feelings to help the reader understand the sensory experience better.
• Onomatopoeia : Use words that imitate the sound associated with an object or action, such as “sizzle” or “pop,” to help your reader connect with the sensation of the smell.
• Show, don’t tell : Rather than merely stating that a character can smell something, describe the actual scent, the effect it has on the character, and the resulting emotions.

By following these guidelines, you can effectively describe smells in your writing, engaging your reader’s senses and creating a more immersive experience.

Examples of How to Describe Smells

Using smells in character descriptions.

To create vivid characters, writers can use descriptions of scents to convey personality traits and evoke emotions in the reader. For example, you can describe a character’s personal fragrance, such as earthy, floral, or crisp. These words can help characterize them as masculine, feminine, or even androgynous.

Here are a few examples of smells used in character descriptions:

• Her scent was a delicate mixture of lavender and vanilla, making her presence soothing and comforting.
• He carried the unmistakable aroma of fresh pine, evoking feelings of being in a forest.
• Their scent was a confusing blend of citrus and cinnamon, giving them an air of mystery and unpredictability.

Setting the Scene with Scents

In addition to character descriptions, you can use smells to help set the scene or create a mood in your writing. Descriptions of scents can transport your reader to different environments, providing an immersive experience and enriching your narrative.

Here are a few examples of using smells to establish a scene:

• The sweet smell of freshly baked pastries greeted her as she entered the cozy bakery.
• A salty sea breeze filled the air, transporting her back to summer days spent at the beach.
• The pungent odor of gasoline and burning rubber filled the bustling garage, immersing the reader in the world of auto repairs.

While describing smells in your writing, remember to keep the tone confident, knowledgeable, neutral, and clear. In doing so, your descriptions will be more effective and enriching for your readers.

Common Pitfalls in Describing Smells

Overuse of adjectives.

One common pitfall in describing smells is the overuse of adjectives. While adjectives are necessary to convey the intensity or quality of a smell, too many can leave the reader overwhelmed and confused. It’s important to strike a balance and use adjectives judiciously. Try to focus on choosing a few strong, specific adjectives that accurately convey the scent you’re describing. Using too many adjectives can also make your writing appear less polished and professional.

Describing Smell without Context

Another issue writers encounter when describing smells is neglecting to provide context. Smells don’t exist in isolation; they are often tied to a specific setting or situation. To make your descriptions more effective, try to include contextual details that will help the reader imagine the scent more vividly. For example, instead of simply describing a smell as “musty,” you might indicate that the musty odor is reminiscent of a damp, old basement, which not only grounds the scent in a physical space but also allows your reader to better visualize and understand the smell.

Ignoring the Readers’ Experiences and Associations

Finally, it’s important to consider your readers’ experiences and associations when describing smells. People’s interpretations of scents can vary widely due to their personal experiences and cultural backgrounds. What smells delicious to one person might be off-putting to another. In your descriptions, try to take these differences into account by using relatable, universal examples that most readers will understand. At the same time, avoid using highly subjective or personal associations that may not resonate with everyone. By keeping the reader in mind and considering their experiences, you can create more effective, engaging descriptions of smells in your writing.

Frequently Asked Questions

How can i effectively convey scents in my writing.

To convey scents effectively in your writing, you should provide a vivid and specific description that helps the reader imagine the smell. Think about the different aspects of the scent – its intensity, its duration, and the sensations it evokes. Make connections with memories or emotions, and use sensory terms and similes to enhance the description.

What are some sensory terms used for describing various smells?

Sensory terms used for describing smells can be grouped into different categories, such as

• Floral (e.g., rose, jasmine)
• Fruity (e.g., citrus, berries)
• Earthy (e.g., damp soil, petrichor)
• Spicy (e.g., cinnamon, cloves)
• Sweet (e.g., vanilla, caramel)
• Pungent (e.g., ammonia, vinegar)

These terms help you create a more detailed and immersive experience for your reader.

What are some ways to describe a compelling fragrance?

When describing a compelling fragrance, consider:

• Its main scent (e.g., lavender, sandalwood)
• Its subtler notes (e.g., hints of lime or vanilla)
• The way it evolves over time (initial burst, heart notes, and base notes)
• The feelings it evokes (e.g., warmth, calm, energy)

Use comparisons and similes to make the description relatable and engaging.

How can I illustrate the smell of a person or an environment?

To illustrate the smell of a person or an environment, focus on the most characteristic and dominant scents associated with them. For a person, consider their perfume, body odor, or even the laundry detergent they use. For an environment, think of the combination of smells present, such as the saltiness of the sea, the vegetation, or the exhaust fumes in a city. Use sensory details and create a vivid description that transports your reader to the scene.

What phrases can be used to describe unpleasant odors?

Here are a few phrases you can use to describe unpleasant odors:

• Rancid or sour
• Musty or stale
• Overpowering or suffocating
• Acrid or sharp
• Fetid or rotten

Be creative with your language and comparisons to help your reader understand the intensity and nature of the unpleasant odor.

How can I incorporate the sense of smell into descriptions of natural surroundings?

To incorporate the sense of smell into descriptions of natural surroundings, focus on the most characteristic scents of the setting. Think about the smells associated with the place – the earthy aroma of a forest, the fresh scent of a meadow, the salty tang of the ocean, or the fragrant blossoms in a garden. Use descriptive language and draw connections with memories or emotions to enrich your depiction and engage your reader.

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