Smell You Later: The Weird Science of How Sweat Attracts

Smell is often dismissed as the least important sense. But it’s the funk that draws us together

A photograph of a woman in a workout top sweating

At Oktyabrskaya metro station, in Moscow, a towering bronze statue of Vladimir Lenin glares along Krymsky Val Boulevard toward Gorky Park. Below Lenin’s feet, among the proletariat entourage, a sculpted woman stands with one arm raised in triumphant solidarity, her armpit exposed and victorious. I decide that this is a good omen. I am, after all, en route to a smell-dating event, where Russians will be judging the attractiveness of my armpit aroma.

Billions of dollars are spent every year trying to avoid this exact judgment. For many people, body odour is so unappealing that they mask it with perfumes, deodorants, and antiperspirants. But what if our obsession with blocking BO is interfering with important lines of communication, those helpful messages aromas send about anxiety, illness, or even romance? When we spray or roll on a product, could we be blocking our chances of finding love, of finding the person—or perhaps people—who might desire us even more because of our scent?

In this era of swiping left and right in the search for a tryst or a soul mate, smell dating operates on a more analog premise. Instead of swiping, the strategy is wiping: namely, one’s perspiration onto a cotton pad. The premise is straightforward: smell-dating contenders work up a sweat doing high-intensity exercise, their perspiration-rich cotton pads are collected and placed in anonymous containers, and everyone lines up to sniff through the smelly samples. Participants then secretly rate their top preferences and give their picks to organizers, who reveal the matches. Like on the dating app Tinder, a match occurs only when two individuals pick each other’s pong.

The only criterion for a romantic match is scent, which is about as logical as any other dating filter. I mean, who cares if you both share a love of taxidermy, say, or the novels of Haruki Murakami? You’ll eventually smell the body odour of your lover, and it’s probably going to be a make-or-break moment. Smell dating skips to the chase (or, more accurately, it entirely skips the chase) and uses body odour as the first elimination round for mate selection—or date selection, at any rate.

There would be several afternoon and evening smell-dating rounds in the city’s most bustling green space, Gorky Park, as part of a larger science-and-technology festival that takes place over a weekend in May. Random people wandering around the park, science nerds attending the festival, and those attracted to the event after seeing it advertised in local media would all participate—or at least that’s what Olga Vlad, the event organizer, told me. This being Russia, people who match up at the smell-dating event would be given exclusive entrance bracelets to a nearby VIP lounge tent so that couples could get to know each other over free, all-you-can-drink vodka cocktails.

A tall German woman with impossibly straight hair and a friendly smile adds my name to the list, hands me some wet wipes, and instructs me to remove the deodorant in my armpits and any other perfumed products I might have put on today.

About forty people are milling around. A twenty-seven-year-old woman named Sofya, wearing a blue bomber jacket and a headband composed of tiny red rosebuds, is surveying the crowd. I ask whether she has ever been attracted to someone on the basis of body odour. “Yes, that’s the only way I choose a partner. I prefer that, when my partner wears no deodorant, that he smells okay. I have been repelled by a man’s body odour.” Sofya gives me a significant look that I don’t know how to interpret.

“I have a question for you,” Sofya says. “Have you ever been on the Moscow subway in the summertime? The smell of so many bodies is intense. It’s terrible. I think this is the most important problem our government should solve,” she adds with an ironic smirk. “But, seriously, body odour is important for finding a partner. Well, if we are talking about a serious partner, I prefer to speak first. But, when it is about sex, I need to like his smell.”

Alexey, thirty-one, a short muscular man in a tight white T-shirt, says that a woman’s natural smell is “potently important for any relationship. But that’s probably because I have a big nose,” he adds, pointing to his robust aquiline specimen.

Anne Maria is a twenty-one-year-old Italian exchange student who wants to try meeting Russians offline. Sergey and Anya are already a couple: they want to see if they can select each other’s scents in the smell-dating game and be matched by organizers. (This, I think, is a perfect way to doom a relationship.) Alek is an impossibly shy, extremely tall twenty-year-old with a blond flop of hair who tells me that he really doesn’t know if he likes a woman’s natural body odour because he doesn’t have much experience with dating.

Scrutinizing the crowd with furrowed eyebrows is Dmitri, a swarthy, serious thirty-year-old with a fashionably thick beard. He says he eats raw garlic daily for its putative health benefits, as suggested by his mother. “For three years I only use unscented soap for kids and no deodorant. And there’s been no difference to my love life,” he asserts. When I ask why he eschewed personal care products, Dmitri replies, “Perfumes have made civilization false. Before, when humans lived in small groups, the village community could smell each other. The smell of other humans was a good smell, it meant safety, it was your community.”

From birth, we rely on our sense of smell to learn the body odour of individuals we love or need the most. A newborn baby, though helpless and immobile, will scooch preferentially toward their own birth mother’s odour when breast-milk pads from four different women are placed in the four corners of their cradle. Likewise, a mother can identify her own newborn baby by smell just a few hours after birth. (A parent who didn’t give birth can do it too, after seventy-two hours.) Newborn noggins inspire many to inhale deeply. When researchers sampled the body odours from two-day-old newborns and gave them to women (both mothers and nonmothers) to sniff, the smells activated the reward centre of the brain. One wonders whether our brains reward those who sniff as part of a strategy for helping us learn the odour of our community’s newest member.

Sniffing the odours of our loved ones—whether consciously or unconsciously—continues throughout our lives. Siblings and married couples are able to correctly identify the smell of people with whom they cohabitate. Even adult siblings who haven’t seen (or smelled) each other for more than two years can still correctly recognize their brother’s or sister’s unique odour print, the signature mixture of chemicals floating off their bodies.

The importance of odour for social cohesion is perhaps best exemplified by the challenges of those who cannot smell. People with anosmia—the inability to smell—often face relationship challenges: men without a sense of smell have fewer sexual partners while nonsmelling women are insecure in their relationships. Both are more prone to getting depressed. Meanwhile, some research suggests that empathetic people are more likely to remember the odour of another person.

Our sniffing abilities and their role in establishing and maintaining social structures can be surprising to some, likely because the human sense of smell has long been belittled by scholars: the father of transcendental idealism, Immanuel Kant, thought life would be better if we all just held our noses so that they were shut off from the outside world. “Which organic sense is the most ungrateful and also seems the most dispensable? The sense of smell. It does not pay to cultivate it or refine it . . . for there are more disgusting objects than pleasant ones (especially in crowded places), and even when we come across something fragrant, the pleasure coming from the sense of smell is fleeting and transient.”

Throughout history, many thinkers have argued that vision is a much more civilized way of experiencing the world; using our noses seemed animalistic, vulgar, backward. If humans sniffed one another as dogs do, how could we consider ourselves above them? How could we consider ourselves enlightened?

During the 1800s, Western culture morphed its distaste for olfaction into a belief that the human sense of smell was mediocre and superfluous. To negate the possibility that humans might be uncivilized smellers, we bought in to a convenient fib: that the human sense of smell wasn’t very good. More recently, Rutgers University neurobiologist John McGann penned a fact-check in the prestigious journal Science: “Poor human olfaction is a 19th-century myth.” McGann blamed a neuroanatomist called Paul Broca, in particular, for this falsehood. Broca had classified humans as “nonsmellers” not as a result of sensory testing but because of his unsubstantiated belief that the human brain had evolved free will at the expense of our olfactory system. Everybody has seen dogs become so entranced by a smell that they bound off in seemingly uncontrolled pursuit of some inordinately desirable odorous objective. Surely we’re better than that?

But these two qualities (olfaction and self-determination) are not mutually exclusive. We don’t need to nix our noses to be in control of the rest of our body. And, in reality, humans have an excellent sense of smell. Our olfactory bulb, which is responsible for detecting odours, “is actually quite large in absolute terms and contains a similar number of neurons to that of other mammals,” McGann has written. “We can detect and discriminate an extraordinary range of odors, we are more sensitive than rodents and dogs for some odors, we are capable of tracking odor trails, and our behavioral and [emotional] states are influenced by our sense of smell.”

One of the more delightful proofs that humans can track odour trails is thanks to a group of undergraduates from the University of California, Berkeley. In 2007, a neuroscientist named Noam Sobel, then on faculty there, blindfolded the students, put them in a field, and told them to sniff out a trail of chocolate, like a hound tracks a hare. Sobel and his colleagues showed that humans (or at least hungry students) can track scents like any other self-respecting mammal and that we do so by making comparisons between the odours floating up into one nostril versus the other.

But there’s a big difference between identifying a familiar smell and deducing new information about an unknown person from that person’s body odour. Accurately intuiting invisible facts about a stranger on the basis of that person’s aroma would require either that we have learned odour X corresponds to characteristic Y or that humans have some sort of inherent, genetically encoded knowledge that odour X corresponds to characteristic Y. Furthermore, deducing anything from somebody else’s body odour would require that we lean in and sniff them, an activity that is considered both awkward and creepy in most social circles.

Or is it?

Most human greetings have involved a moment or two of increased proximity wherein we can, at least theoretically, take in the odour of another person. Hugging and cheek-kissing are obvious opportunities to sniff one another, especially in parts of the world, such as Europe and the Middle East, where cheek-kissing involves pecking back and forth multiple times. (Folks in Corsica greet one another with as many as five consecutive cheek kisses.)

Bowing forward, as the Japanese and Korean people do, also brings two individuals within sniffing distance. And then there’s the handshake. It may not bring your nose close to a new person, but it results in a hands-on collection of a new person’s sweat and other odours found on the hand—which can then be sniffed later, at one’s own discretion. At least, all this was true before COVID-19.

Sobel also conducted a fascinating experiment with his graduate student Idan Frumin to see what people did with their hands after a handshake. Their team secretly videotaped people after they shook the hand of someone new, someone they had just met for the first time. Here’s their delicious discovery: a few seconds after the handshake, the experimental subjects would inevitably sniff their own hands to gain some odorous information about the new person.

“When we showed them the videos, many of the subjects were completely shocked and disbelieving,” Frumin told me. “Some thought we had doctored the videos—not that we had the computing power or the expertise to do so.”

When the new individual was of the same gender (in this and many studies on odour signalling in humans, scientists have primarily focused on heterosexual individuals, and they have not included research subjects who are trans or nonbinary, or mentioned if they have), the subjects sniffed their own shaking hand twice as much as before. In contrast, after handshakes across different genders, subjects more than doubled the amount of sniffing they did of their own nonshaking hand. The scientists speculate that sniffing the hand that contains residue of a person of the same gender could deliver information about potential sexual competitors. In the animal world, many species have as avid an interest in the odours of their sexual competitors as they do in the odours of their potential conquests. “A handshake is a way to transfer that information and have it, well, in the palm of your hand,” Frumin says, “to sniff at your convenience.” When Frumin now goes to conferences, he sometimes stands back and watches people unconsciously sniffing. “Sometimes I catch myself doing it too. People tell me I’ve ruined handshakes for them, that they’ve become very self-conscious about shaking hands, especially with me.”

These days, we want our life mates to satisfy our intellectual, emotional, and physical needs. But, evolutionarily speaking, for propagation of the species, all humans need is someone with compatible-enough genes that our offspring have a decent chance at survival, at least long enough to procreate themselves, so that our DNA can be passed on to future generations.

The best proof of this comes from a study published by Claus Wedekind in 1995, when he was a graduate student. Wedekind (now on the faculty at the University of Lausanne) showed that women can sniff out a genetically compatible mate—or at least mates with compatible immune systems. Female test subjects were asked to rate the attractiveness of odours emanating from T-shirts worn for two days by anonymous men. Meanwhile, blood samples were taken from everyone for an analysis of their DNA, specifically of a set of immune-system genes called the major histocompatibility complex (MHC).

These genes are involved in helping immune cells learn to recognize pathogenic foreign invaders. As it turned out, women preferred the odour of men whose MHC genes were different enough that any shared offspring would likely have healthy immune systems.

At the time Wedekind started his work, researchers already knew that some animals selected mates along these lines. Mice were found to dip their noses into one another’s pee to suss out things such as gender and virginity status. On the basis of urine odour, rodents preferentially mated with those who had dissimilar MHC types.

“If you are in danger of mating with a close relative because you don’t know them socially, which happens in mice, then a cue that helps you to identify how close you are related to another mouse would help you avoid inbreeding and all the negative consequences that come from it,” Wedekind says.

“Humans used to live in small groups over several generations, so there was a certain danger that the few individuals available for mate choice could potentially be relatives. The mother of someone is always obvious, but the father is not always so clear. So there was always a danger of having a baby with your relative. And a cue that would help avoid that would then provide an evolutionary advantage. That could be why we initially developed these preferences,” Wedekind explains. “But this doesn’t make much sense now,” he quickly adds, because the pool of humans to mate with is now enormous, and most people know their family trees. Subsequent research has generally confirmed Wedekind’s original work, but attempts to tease out nuances or show that this MHC effect has a major impact in modern human mate choices have been mostly disappointing.

There’s still a serious issue with the MHC studies: How do we smell these immune-system genes located deep in the nuclei of our cells? One might be tempted to propose that the MHC genes code for MHC proteins that emerge in sweat and float up off a body and into another person’s nose. If this were true (and nobody has checked that it is), there’s a big problem. These MHC proteins are enormous, much larger than the odour molecules that spontaneously float up and out of our sweat—so large and bulky that one evaporating off a human body would be like a hippopotamus spontaneously evaporating out of a sub-Saharan lake.

Which is not to say that I don’t believe the end result of the MHC science in humans: I have no reason to doubt that our sexual predilections may be tuned by the immune systems of our potential mates. But it’s important to remember that scientists haven’t figured out the details of how precisely that message is communicated. Wedekind himself bemoans the fact that this part is a black box. “It bothers me, too, that we haven’t tracked down the mechanism,” he says.

Yet there is other evidence that our perspiration carries messages that may lubricate the path to love and sex. One of the most oft-quoted studies (by the lay public) to this effect took place in a strip club. The scientists, based in New Mexico, wanted to find out if a woman was more attractive to (straight) men during the most fertile period of her menstrual cycle (called estrus) thanks to her body odours, something that’s true for many other female mammals.

When the scientists tracked the tips from lap dances and the women’s fertility statuses, they found that the dancers earned the most tips when they were most fertile, in the estrus window of their cycles. Although the researchers didn’t test their body odours, they argue that something in a lap dancer’s scent was communicating to her clients that she was fertile. Each dancer presumably wore similar outfits, did the same routines, and had the same personal motivation to earn good tips throughout the entire month. Yet, somehow, the spike in a dancer’s luteinizing hormone, which signals the ovaries to release an egg or two, was communicated beyond her body. And this biochemical message was appreciated (one assumes unconsciously) by men who purchased lap dances.

“Okay everyone, let’s work up a sweat!” On a patch of Gorky Park grass, Alanna Lynch is wielding a megaphone, her dark curly hair held back with a green head scarf. She’s wearing a brown tank top, black yoga pants, and bright-pink sneakers that flash up and down as she jogs in place to rouse the crowd. The group of aspiring smell daters stops milling around and forms a semicircle around her on the lawn. After reminding everyone that they should have wiped off deodorants, perfumes, and antiperspirants, she cheers, “Let’s do this!” and begins to lead a calisthenic routine “guaranteed to make everyone sweat.”

At the end of Lynch’s routine, we’re handed little cotton pads. “Make sure you wipe your chest and armpits,” Lynch says into the megaphone. Each of us then puts our damp cotton pad into an individual numbered glass jar. “Don’t forget your number,” Lynch says. “That’s how you’ll know if you have a match.” I see Alek, the shy young man, sniff his cotton pad before putting it into his jar. “Smells like you?” I ask. He nods. “Definitely,” he says with a smirk.

After everyone has handed over the jars containing our sweaty cotton pads, the organizers line up the jars on a table. Then there’s a swarm as everyone crowds over to sniff the samples, which have not been separated by gender or sexual orientation.

I take a sniff from a jar. It is ripe, metallic, and goaty. Like the odour of a hormonal teenager in the full throes of puberty—plus exercise. I have no desire to sniff that jar ever again. The next jar’s scent is barely noticeable, or maybe that’s because my nose’s odour receptors have gone on strike after the hormonal adolescent pong. I step away and breathe a bit of normal air for a few seconds and then return to the same jar. I notice a faint smell of onions and grass and earth, like lying in a field on a summer’s day. Quite pleasant actually. I note the number: twenty-three.

As I progress through the jars, there’s a pretty even split of samples that don’t have much of a scent and ones that I can smell but aren’t what I’d consider particularly pleasant. Not particularly unpleasant either, but just not all that appealing to me. Many jars deliver aromatic jolts of onion and goat—two of the most common top notes found in human armpit odour. One jar smells like curry. Another like cabbage soup.

I note the numbers of a few samples that I’m on the fence about because I’ve got to give the organizers a list of my five favorites. And then I hit jar fifteen. It smells to me like sex epitomized. When I sniff again, trying to tease apart the aroma profile, I can detect the standard goaty, oniony background odours of another human, very similar to all the other samples. But something in that mix made me want to sniff again, ASAP. The odour didn’t send me into an erotic paroxysm, but it was fundamentally appealing: it triggered an instant reminder that there’s this great activity one can engage in with another person and it’s called sex.

In my reporter’s notebook, I wrote down “15!!!!!!!,” devoting an entire page to this piece of information. I also wrote the number on the sheet of paper I returned to the organizers, at the head of my list of favourite odour samples. As I handed in my picks, a sudden twinge of adolescent insecurity passed over me: Would anyone on my list reciprocate? Would I find a match and score a coveted entry bracelet to the VIP cocktail lounge with my potential paramour?

It’s strong reactions like mine to jar fifteen that rouse belief in human sex pheromones, odorous chemicals that catalyze copulation. Insects have them, amphibians have them, mammals have them, so why wouldn’t we?

Human pheromones have been dropping suggestive hints that romance is in the air but never quite delivering the goods to the scientists who’ve been in hot pursuit for decades. Nobody has been able to pluck out a human pheromone from the thousands of molecules floating off human bodies despite enormous effort and a lot of tantalizing indirect evidence. Which doesn’t mean they don’t exist. It just means that nobody’s found the chemical culprits yet, like they have for animals as varied as pigs and moths. Case in point: bombykol, the first pheromone discovered in silkworm moths, in 1959. Bombykol is a quintessential example of sexual instant gratification. When a female moth has a hankering for romance, all she needs to do is release bombykol in the direction of her desired Romeo and he’ll fly over to mate with her.

Another legit pheromone is produced by the male boar, curiously enough, in his saliva. These hairy hogs just need to wander over to a sow in heat and breathe heavily in her direction. When she gets a whiff of that pheromone, the female spins around, lifts up her rear, and presents it to the male so he can mount.

Even if humans produced such a pheromone in our evolutionary past, nowadays its potency has certainly been dialled down by all sorts of competing impulses. We’ve become highly visual creatures: how a prospective sexual partner looks plays a significant role in whether we try to bed them. And we’ve evolved agency in our sexual decision making. Although it can sometimes be a challenge, humans can exert self-control in matters of sex thanks to some mix of decency, social pressure, and fear of legal repercussions.

Given that sex pheromones are molecules that typically inspire members of a species to behave like progeny-making automatons, there’s a disconnect between the strict concept of a sex pheromone and the subtle evidence that humans are using body odour to learn about and develop preferences for one another. Many scientists working in this field never use the words human pheromone when talking about their work. Researchers who have devoted decades of their lives to studying human chemical communication avoid the p-word, opting instead to use terms such as human chemical cues or chemical signals or social chemosignals. Because whatever information being transmitted off human bodies through the air and into our noses may be influencing our decision making, but it’s not dictating it.

“We have a problem where we all sort of agree that there’s something there in humans but we don’t know how to label it,” says Johan Lundström at the Karolinska Institute, in Stockholm. “The good thing with pheromone is people know what you’re talking about. You stop someone on the street and they’ve heard of a pheromone. But it’s completely overused commercially. And the general public associates the word pheromone with sexual mating. But very few pheromones [in other animals] have to do with mating. They may assist and inform in mating but they don’t induce horniness. The word pheromone has been tainted with sex.” And, when you know what an honest-to-goodness sex pheromone really does, it’s hard to call what we see happening in humans by the same name.

“We’ve got matches!” Back at the smell-dating event, another organizer is listing jar numbers of people who matched up. I pull out my number from my pocket: twenty-two.

As matching numbers are called out, a motley group of people begin to pair up.

“And number twenty-two…” That’s me! I step forward and hold my breath. “You are matched with number twenty-three!” I look at my notes. Damn. Not number fifteen, the person who reminded me of pure sex. Twenty-three is the person with the delicate body odour, like mown hay, the one that was pleasant, comforting.

I look around and there she is: honey-blond hair, hazel eyes, wearing a pair of tight jeans and a cool camel-coloured leather jacket. I have been matched with a vision. She is undeniably gorgeous. Who cares if I don’t actually prefer women—I feel like I have won the smell-dating contest. I laugh in delight, walk over, and say awkwardly, “I think we are a match? I’m number twenty-two.” She flashes me an open, friendly smile and says, “Hi, I’m Anastasia.” She tells me that she works in fashion as a handbag importer and that she writes restaurant reviews on the side.

“Wait a second,” I say. “You’re a foodie? Someone with a critical nose and palate picked my BO?” She laughs and we start chatting about the other things we’ve seen at the science festival. Out of the corner of my eye, a tall gangly guy in his thirties approaches wearing a button-up shirt. His nametag says Ivan and he gives Anastasia a look of trepidation. She smiles warmly. “Oh, you’re my other match, aren’t you?”

Wait, what? I have competition? Anastasia has been matched with both of us, but Ivan and I have been matched only with Anastasia. “Looks like I’ll have to fight you for her,” I say with a grin, fists raised.

“Okay, fine,” he replies. “But let’s drink at the VIP lounge first and fight later.”

The yellow VIP tent is packed. The structure’s white canvas walls are shaking precariously from the sound system’s heavy bass. Dozens of people are propping themselves up against tall white tables. Others recline on couches placed along the tent’s perimeter.

Alek, the tall skinny guy with blond floppy hair and no dating experience, is trying to chat with a short girl-next-door type wearing a T-shirt printed with hearts and the word love. I detour over to them. “We are both students!” Alek exclaims, as though this is a match made in heaven. He is beaming so widely I think he might lose his balance. She also nods enthusiastically. Now here is some real chemistry. Not wanting to disrupt it, I smile, raise my glass toward them, and circle back to my own group.

Ivan, my competitor for Anastasia, is talking about his work at a dog shelter in his free time. “I give up,” I say, bowing to him. “There’s no way I can compete with hobbies as virtuous as that.”

“Don’t give up too soon,” Anastasia replies flirtatiously. “Well, at least not until my husband comes by to pick me up.”

Ivan’s face drops. Dude, I think, neither of us ever really had a chance.

I finish off my cocktail, wish Ivan and Anastasia luck in life and love, and stumble out of the VIP tent in search of food. Sergey and Anya, the long-time couple, appear on my path, also heading toward the park’s exit. “Wait, aren’t you going to the VIP lounge?” I ask them.

“We can’t. No VIP bracelet because we didn’t match. I recognized her scent and picked it, but”—and he turns to glare at his girlfriend—“she didn’t pick me!”

Excerpted from The Joy of Sweat: The Strange Science of Perspiration by Sarah Everts. Copyright © 2021 by Sarah Everts. With permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.

Sarah Everts
Sarah Everts holds a master’s degree in chemistry and has written for Scientific American, Smithsonian, New Scientist, and the Economist. She teaches journalism at Carleton University and lives in Ottawa.