Do humans really have a body scent? Do we really find someone of the opposite sex “sexy-smelling”? And what exactly is the relationship between perfume and body scent?
Let’s talk about “smell psychology”—looking at the subtle interaction between perfume and the odors our own bodies produce, from a psychological perspective.
Let’s talk about body scent first, and perfume afterward.
Let me start with a question: why do you think people fall in love at first sight? The first instant you see a woman or a man, your face flushes, your heart races, and you’re smitten—is it because they’re exceptionally good-looking? Their presence is dazzling? Their expression is adorable? Any of those could be true. But there’s another possibility that’s easy to overlook: they smell sexy—you were actually attracted to the other person’s scent without realizing it.
Can the scent coming off the human body really have that kind of lethal appeal?
It can. Although the scent produced by the human body seems extremely faint, it may play a surprisingly important role in mate choice and attraction between the sexes.
In one study, Brown University olfactory psychologist Rachel S. Herz listed all kinds of qualities in men, from the physical to the psychological, from looks to personality, and asked some women to rate which qualities mattered most when choosing a partner. The results showed that among all the traits a man could have, body odor carried a very high weight. If a woman felt that a man’s naturally occurring body odor smelled “wrong,” then no matter how dazzling his other qualities were, she wouldn’t want an intimate relationship with him.
So why is body odor so important? What information does the scent of another person’s body actually convey?
The information in body scent is actually incredibly rich.
For example, one study gave women T-shirts worn by a group of men to smell. The women generally rated the shirts as better-smelling when they had been worn by men with more symmetrical bodies and facial structures. Men with more symmetrical bodies and faces of course look more handsome, but more importantly, this also suggests that their genes are more robust and their bodies healthier. The women could pick out these men based on scent alone.
Men, in turn, are also sensitive to women’s body odor. In another experiment, researchers had women wear T-shirts at different stages of their menstrual cycles, then gave the shirts to a group of men to smell. The men found the scent sexier and more pleasant when the shirts had been worn by women in the follicular phase. The follicular phase is the stage when an egg develops toward maturity, which means that men could identify women’s fertility window with surprising precision through scent.
See? We can smell “health” and “fertility potential” on another person. But those signals may not even be the most important ones. The most important signal we can pick up from another person’s scent is actually their MHC genotype.
MHC is short for major histocompatibility complex. MHC genes largely determine a person’s immune traits. People with different MHC genotypes have different levels of resistance to various microbes and pathogens. If our MHC genes are very different, then when one virus is going around, you might be completely fine while I get sick—but the next time a different virus comes along, the situation might reverse.
The fascinating thing is that when men and women smell each other, they often find the people who are “sexier-smelling” to be those whose MHC genotypes differ greatly from their own.
Swiss zoologist Claus Wedekind conducted an experiment in which, once again, women were given T-shirts worn by men and asked to rank the scents according to how much they liked them. The women preferred the scents of men whose MHC genes showed the greatest difference from their own. The scents of these T-shirts were also more likely to remind the women of the body odor of their current or former partners. In other words, by smelling these scents, the women unconsciously developed a liking for men whose immune traits complemented their own. And this preference is quite stable and specific—the scents of successive boyfriends tend to be similar, after all.
So when I said at the beginning that you might fall in love at first sight with a handsome man or beautiful woman walking toward you, maybe the two of you simply “smelled right” to each other. Your nose was secretly telling you that the person approaching had an MHC genotype highly complementary to yours, triggering that feeling of love at first sight without your conscious awareness.
But why does this happen?
The most reasonable explanation, of course, is that having children with someone whose MHC genes differ greatly from yours increases the diversity of their immune traits. If I have kids with someone whose MHC genes are more or less like mine, we can only produce a bunch of kids who are more or less alike. But if I have kids with someone whose MHC genes differ greatly from mine, we can produce a whole string of immune-system oddballs, each with a different set of traits. That way, when some deadly microbe comes along, more of my descendants may survive, and our family is less likely to get wiped out altogether.
So don’t let the low profile of smell fool you: it’s actually incredibly powerful, and may be quietly deciding all sorts of things.
But here’s the problem: natural body odor is so important, yet these days it’s often mixed with another artificial scent that’s much stronger. That artificial scent, of course, is perfume.
If perfume is so strong, does it cover up our own body scent?
You may have heard the story that perfume became so popular today, and such a basic cosmetic, because during the Black Death in Europe, French aristocrats were afraid to bathe, so they used huge amounts of perfume to cover up their body odor—and that this gave birth to the modern perfume industry.
But perhaps using a powerful perfume scent to cover up body odor is just a very special case. The Swiss scientist Wedekind, who made an appearance earlier, has come up with another finding recently.
In a new study, he had a group of women smell 32 of the most common perfume ingredients. They were asked to judge how well a perfume containing each ingredient would work if they wore it themselves. Naturally, different women made different choices. But interestingly, Wedekind also tested the women’s genetic sequences and found that women with similar perfume preferences also had very similar MHC genotypes. In other words, women with similar immune traits chose perfumes with similar scents for themselves.
And this result appeared only when they chose perfume for themselves. When the experimental condition was changed to “choosing a nice-smelling perfume for someone else,” the women’s choices had no relationship to their MHC genotypes.
So the researchers speculate that when people choose perfume, they may very well be unconsciously choosing scents similar to their own body odor—perfumes that enhance their natural body scent.
References:
1. If a woman thinks a man’s body odor smells “wrong,” she won’t want an intimate relationship with him:
Herz, R. S., & Inzlicht, M. (2002). Sex differences in response to physical and social factors involved in human mate selection: The importance of smell for women. Evolution and Human Behavior , 23(5), 359-364.
2. Symmetrical men smell sexier (additional note: only women in the ovulatory phase show this preference):
Gangestad, S. W., & Thornhill, R. (1998). Menstrual cycle variation in women’s preferences for the scent of symmetrical men. Proceedings of the Royal Society of London. Series B: Biological Sciences , 265(1399), 927-933.
3. Women in the follicular phase smell sexier
Singh, D., & Bronstad, P. M. (2001). Female body odour is a potential cue to ovulation. Proceedings of the Royal Society of London. Series B: Biological Sciences, 268(1469), 797-801.
4. People of the opposite sex with large MHC differences smell sexier:
Wedekind, C., Seebeck, T., Bettens, F., & Paepke, A. J. (1995). MHC-dependent mate preferences in humans. Proceedings of the Royal Society of London. Series B: Biological Sciences, 260(1359), 245-249.
5. Women with similar perfume preferences also have highly similar MHC genotypes:
Milinski, M., & Wedekind, C. (2001). Evidence for MHC-correlated perfume preferences in humans. Behavioral Ecology, 12(2), 140-149.
6. Ambergris and ambroxide:
Kemp, C. (2012). Floating gold: A natural (and unnatural) history of ambergris. University of Chicago Press.
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