Is it reliable to find a partner through body odor?

Our body odor stores a wealth of biological information, which not only reflects a person's health status and eating habits, but can also be used to judge personality traits. The saying "birds of a feather flock together" is true. Body odor also plays a certain role in mate selection. In one study, women randomly obtained T-shirts worn by men and sorted them according to their preferences for odor. The results showed that the order of odor was consistent with the degree of difference in human leukocyte antigen (HLA). This shows that there are deeper genetic reasons for mate selection through odor, because people will instinctively choose to mate with the opposite sex with a greater HLA difference in order to reproduce better offspring. Of course, many people use perfume to cover up their body odor. Perfume is certainly attractive, but it is actually a double-edged sword.

Written by | Xiaotao

In 1682, Louis XIV brought his royal family to a hunting lodge left by his father. It was called a lodge, but it was actually just a few simple huts. Louis XIV made an expensive renovation to it and planned to settle there. This was a major decision, because France was similar to a nomadic regime before, and the royal family migrated around with the change of seasons and only returned to Paris at a certain time of the year.

This cottage later became the Palace of Versailles.

At that time, Versailles was far from being a suitable place to live in. The renovation work had not yet been completed, and it was said that there were large swamps next to the palace, full of sewage pits and animal carcasses and excrement, and it smelled like a slaughterhouse.

Such a description is inevitably exaggerated, but it shows the dilapidated and dirty Palace of Versailles at that time. When we realize this now, it seems not difficult to understand why Louis XIV was so keen on perfume - whoever lived in such a stinking environment would have to find a way to cover up the unpleasant smell, right?

Figure 1. Louis XIV had a deep relationship with perfume. Image source: perfumesociety.org

Louis XIV was a monarch with a good sense of fashion. The three-piece set of fashionable ladies - perfume, high heels, and wigs - were closely related to him. However, his love of perfume was not necessarily due to his fashion taste. It is said that Louis XIV's personal hygiene was worrying. He took a bath only a few times in his life. In order to cover up the unpleasant body odor, he often sprayed perfume.

So the question is: What causes body odor? Or, what factors affect body odor?

Why do we have body odor?

A more straightforward reason is personal hygiene habits. This is how Louis XIV's body odor came from. We often have this experience: when we sweat a lot, we seem to have an indescribable odor on our bodies. In fact, nearly 99% of sweat is water, and the remaining little is salt and urea. It has no odor itself. The culprit of the pungent odor is the surface microorganisms mixed in the sweat.

Sweat is secreted from sweat glands. There are two types of sweat glands: one is evenly distributed throughout the body and can help people dissipate heat, called exocrine glands; the other is apocrine glands, which are mainly distributed in the armpits, areola, and around the navel. The sweat secreted from apocrine glands is different from that secreted from exocrine glands. In addition to water, salt, and urea, this type of sweat also contains fat, protein and other substances. When the bacteria on the surface of the skin (such as micrococci, aerobic diphtheroids, Propionibacterium, etc.) decompose these substances, they will produce sulfur-containing or ammonia-containing components with pungent odors, so it smells bad; for this reason, the smell of sweat is mainly emitted from places with more apocrine sweat glands.

But sweating isn't the only reason for body odor and differences. There are many different sources of body odor, including some that are weird. For example, eating habits, menstrual cycles, and even illness can affect body odor.

Figure 2. Distribution of exocrine and apocrine sweat glands in the human body | Image source: fitpage.in

What body odor can tell us

Body odor can reveal almost every aspect of a person - it is no exaggeration to say that you can tell a person by his scent.

Figure 3. During a woman's menstrual cycle, there are always a few days when she "smells" more sexually attractive. Image source: Michal Bialozej

In fact, the ability to identify the other party's true colors by body odor is probably a universal law in nature. In the animal world, body odor can be used to distinguish friend from foe, because the odor released from the body can be used as an olfactory clue, which reveals the identity information of the "owner" and the body's metabolic status. Human body odor also has the same function.

We release a large amount of volatile organic compounds (VOCs) every moment, some of which have odors - of course, some do not. Body odor is the result of the combination of these hundreds of odorous gases. These gaseous organic compounds are released through breathing, sweating, or excretions such as urine and feces, and vary with age, eating habits, gender, physiological state, and can even reflect genetic differences. Therefore, body odor is also regarded as everyone's "odor fingerprint."

For example, body odor can reflect a person's eating habits. Studies have shown that eating more meat is more conducive to producing pleasant body odor[1]. Even the physiological cycle can get involved. Women's body odor becomes more charming and attractive during the follicular phase, while men's testosterone levels can make them more fragrant[2]. When we are sick, our metabolism will be disturbed to a certain extent, resulting in the production of some "unconventional" gaseous organic matter, or changing the proportion of each component in the gaseous organic matter under normal circumstances, which will cause our "odor fingerprint" to change. For example, patients with trimethylaminuria will exhale trimethylamine, diabetic patients will exhale acetone, and patients with hepatic halitosis will have methyl mercaptan in their breath. Some infectious diseases may produce unpleasant odors through metabolic pathways, which may come from changes in hormones in the body or from symbiotic bacteria on the skin surface and in sweat and sebum[3]. From the perspective of smell, cholera patients "smell" sweet, and the body odor of acute diabetic patients is a bit like rotten apples[4].

In addition to revealing our health status, body odor also affects our evaluation of personality, but this influence is more or less subtle and we may not even be aware of it.

It must be said that body odor is indeed an extremely complex scientific issue. And if you spray perfume or apply makeup, the problem becomes even more complicated.

Where does the fragrance come from?

Where does the "fragrance" of perfume come from? It is actually a combination of many molecules. When you open a bottle of perfume, you smell hundreds of molecules diffused in the air and then into your nose. The smell of each molecule actually comes from the vibration of the chemical bonds in the molecule. Some molecules have the fragrance of grass, such as cis-3-hexen-1-ol, which is often used as a green leaf note in perfume, while some molecules - such as H2S - have a smell of rotten eggs, because different molecules and different connection methods have their own specific frequencies. (Of course, according to this theory, as long as you find a chemical bond with the same vibration frequency as the molecular bond of H2S, the molecule formed by it will also have the smell of rotten eggs, so according to this principle you can create any smell you want.)

Some people tend to use perfume (or scented cosmetics) to make their body odor smell better. But this brings up a question: after the perfume is mixed with your original body odor, does it really "cover up" it? Or will the two intertwine and mix, presenting a "new body odor"?

In fact, perfume is a "double-edged sword". Although it can block the body's natural body odor, it may also enhance the original body odor. Scientists have found that after spraying perfume, whether the "new body odor" after the smell of perfume and natural body odor are mixed together is better or worse, in fact, it varies from person to person, because perfume will interact with your original body odor, rather than simply covering it up. This is why when buying perfume, we should choose a perfume that can match our own body odor, and not just follow the trend of buying a popular one.

Perfume's charm bonus

We may all have a feeling that if we spray perfume, others seem to look at us differently - this is not an illusion. Many studies have confirmed the role of perfume and scented cosmetics in personality evaluation.

Perfume may affect how attractive others are to us. Studies have shown that if an unpleasant smell appears in the environment, a face that was originally quite attractive will suddenly look unattractive. Other studies have shown that perfume can even influence our judgment of a person's professional ability. For example, during an interview, if you spray a little male perfume, you will be considered more qualified for a management position. Conversely, if you spray a female perfume, the interview result for a management position may be a bit worse[5]. So is perfume definitely a good tool for interviews? Not necessarily. A statistical study involving many positions and many job seekers showed that for female job seekers, spraying some perfume is more likely to help them get an offer, but this conclusion is not obvious among male job seekers[6].

Studies have also shown that body odor plays an important role in forming an impression of a person. People often associate unpleasant odors with undesirable personality traits, and this is scientifically justified [7]. A recent series of studies found that people's evaluations of personality traits (especially extraversion, neuroticism, and dominance in the Big Five personality traits) based on body odor are surprisingly accurate [8].

How are body odor and personality traits connected?

First, we know that human physiological functions and personality traits are related to specific hormones and neurotransmitters, so they can serve as a bridge between body odor and personality, especially for neurotic and dominant personalities [9-11]. Second, some emotions are believed to be triggered by body odor [12], and people who often express a certain emotion may have a corresponding body odor [13]. For example, frequent sweating caused by anxiety and tension may change the body odor of people with neurosis. This is another reason why body odor is associated with personality.

Figure 4. Perfume is sometimes associated with personality evaluations

Genes at work

We can actually change our body odor by changing our eating habits or adjusting our body functions. However, there is one factor that we can never change, and that is genes - genes may be the key factor that makes you smell different from others.

Each of us has a unique body odor, and our sense of smell is sensitive enough. The saying "you can tell a person by his or her scent" is true. Someone once did an experiment: they mixed a pair of twins' T-shirts with a bunch of unrelated people's T-shirts, and then asked the subjects to smell the odors from these T-shirts. The results showed that the subjects could easily identify the twins' T-shirts; and the twins' body odors were so similar that the subjects could even confuse whether the smell they smelled came from the same T-shirt or two [14].

Agnieszka Sorokowska, a scientist who studies human olfaction at the University of Wroclaw in Poland, believes this shows that genes do affect our body odor, so in theory, we can detect genetic information by smelling our body odor.

Figure 5. The subjects can smell which two T-shirts are from a pair of twins, which shows that body odor is inextricably linked to genes.

So, what use is this genetic information hidden in body odor to us?

In one study, female subjects were given T-shirts worn by men and asked to rank their smells according to how pleasant they were. The results were very interesting—the order they ranked was exactly consistent with the degree of difference in human leukocyte antigen (HLA) between themselves and the men [15].

HLA is a protein that helps the immune system recognize which cells belong to the body and which come from the outside (which could be potential pathogens). The gene that encodes HLA is called MHC, which also encodes other proteins that play a role in the immune response, so HLA can be a starting point for scientists to understand what type of protection a person's immune system can provide.

Your HLA profile is likely different from anyone else's - of course, your closest relatives will have more similar HLA profiles. From a genetic and hereditary perspective, having a partner with a different HLA profile can give birth to a child with a greater immune advantage. "If your partner has different genes related to the immune system than you do, then your child may have a better resistance to pathogens," Sorokowska explains.

The female subjects sorted the T-shirts in such a way that the men with the most different "HLA profiles" were placed at the front, and the men with the most similar "HLA profiles" were placed at the back, which actually reflects a genetic preference. Of course, they themselves did not know that it was their genes that made the choice for them.

It is not clear how differences in HLA lead to the pleasantness of body odor. Some people believe that HLA can produce specific substances that can be digested by bacteria on the surface of the skin, so HLA actually regulates body odor by affecting the skin flora.

Understand the science behind body odor, but don’t be blindly guided by it

Do people use the genetic information hidden in body odor to choose a partner? Well, it seems not. A study surveyed 3,700 couples and found that the probability of people choosing their partners based on the degree of HLA difference was about the same as that of random selection[16]. This shows that although we have an "innate" preference for a certain body odor, we do not use it to decide who to marry.

From the perspective of evolutionary biology, the basis for women's mate selection is undoubtedly very important. In most species in nature, females choose males when "marrying", and the basis for "their" selection is ultimately to find the opposite sex with the most advantageous genes, so that they can breed offspring with better traits (nature tells us that eugenics starts with finding men.) This is why most male animals in nature have colorful appearances, can sing and dance, and are good at giving gifts - these are all means for them to show their strong genes.

The connection between body odor preference and genes has spawned a business, with smart businessmen creating a fashion dubbed "T-shirt speed dating" and even developing a "body odor mailing" service. However, can such a service really help single men and women quickly find their ideal partner? Or is it simply a waste of money?

Here we need to understand a kind of psychology, that is, in real life, although we do prefer something, we do not necessarily make choices based on this preference. This is because real life situations are very complicated. For example, based solely on body odor, we can make an evaluation of personality traits. We may judge based on body odor that "well, this person has a good temper", but when we see a photo and a body odor sample at the same time, we may think "although this person has a good temper, that person is obviously more handsome", and then we fall into a difficult situation of choosing. Sorokowska even believes that although judging personality based on body odor is more accurate and reliable, it is simpler to look at the face, and human nature often chooses the simpler (not necessarily more correct) option.

In another study, Mehmet Mahmut, a smell and odor psychologist at Macquarie University in Australia, found that the body odor of unmarried men is stronger than that of married men[17]. He speculated that this may be because the higher the testosterone level, the stronger the body odor, and testosterone levels are related to age. Married men are generally older than unmarried men, so their testosterone levels are relatively lower and their body odor is lighter.

At this point, we seem to be able to sense what millions of years of evolution want to tell us through body odor, and the information about a person's reproductive ability seems to be written into the body odor. However, should we "obey" the command of body odor and choose the partner that our genes prefer?

If you just want to find a mate with superior genes, then you should pay attention to the body odor of the opposite sex. But love is complicated, and there is no need to pay too much attention to body odor - after all, we have spent a long time evolving and have already become the person implied by body odor.

References

[1] https://www.sciencedirect.com/science/article/abs/pii/S1090513816301933

[2] https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1439-0310.2006.01125.x

[3] https://doi.org/10.1093/jb/mvr090

[4] https://academic.oup.com/jb/article/150/3/257/867730?login=true

[5] https://doi.org/10.1002/ejsp.123

[6] https://doi.org/10.1037/0021-9010.68.4.709

[7] https://doi.org/10.1016/j.paid.2013.02.026

[8] https://doi.org/10.3389/fpsyg.2016.00530

[9] https://doi.org/10.1210/jcem-73-5-1016

[10] https://doi.org/10.1006/hbeh.1995.1025

[11] https://doi.org/10.1111/j.1467-9280.1995.tb00521.x

[12] Fialová, J., and Havlíˇcek, J. (2012). Perception of emotion-related odours in humans. Anthropologie. 50, 95–110.

[13] https://doi.org/10.1002/per.848

[14] https://pubmed.ncbi.nlm.nih.gov/16162644/

[15] https://www.sciencedirect.com/science/article/abs/pii/S0018506X18300539

[16] https://royalsocietypublishing.org/doi/full/10.1098/rspb.2020.1800

[17] https://www.frontiersin.org/articles/10.3389/fpsyg.2019.00261/full

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