Does Your Nose Help Pick Your Friends?

Human beings maintain the polite fiction that we’re not constantly smelling one another. Despite our efforts to the contrary, we all have our own odors, pleasant and less so, and if we are like other land mammals, our particular perfume might mean something to our fellow humans.

Some of these, like the reek of someone who hasn’t bathed all month, or the distinctive whiff of a toddler who is pretending they didn’t just fill their diaper, are self-explanatory. But scientists who study human olfaction, or your sense of smell, wonder if the molecules wafting off our skin may be registering at some subconscious level in the noses and brains of people around us. Are they bearing messages that we use in decisions without realizing it? Might they even be shaping whom we do and don’t like to spend time around?

Indeed, in a small study published Wednesday in the journal Science Advances, researchers investigating pairs of friends whose friendship “clicked” from the beginning found intriguing evidence that each person’s body odor was closer to their friend’s than expected by chance. And when the researchers got pairs of strangers to play a game together, their body odors predicted whether they felt they had a good connection.

There are many factors that shape whom people become friends with, including how, when or where we meet a new person. But perhaps one thing we pick up on, the researchers suggest, is how they smell.

Scientists who study friendship have found that friends have more in common than strangers — not just things like age and hobbies, but also genetics, patterns of brain activity and appearance. Inbal Ravreby, a graduate student in the lab of Noam Sobel, an olfaction researcher at the Weizmann Institute of Science in Israel, was curious whether particularly swift friendships, the kind that seem to form in an instant, had an olfactory component — whether people might be picking up on similarities in their smells.

She recruited 20 pairs of so-called click friends, who both characterized their friendship this way. Next she put them through a regimen that’s common in human body odor research: Stop eating foods like onions and garlic, which affect body odor, for a few days. Lay off the after-shave and deodorant. Bathe with an unscented soap provided by the lab. Then put on a fresh, clean, lab-provided T-shirt and sleep in it so it gets good and smelly, before handing it over to the scientists for review.

Ms. Ravreby and her colleagues used an electronic nose to assess the volatiles rising from each T-shirt, and they had 25 other volunteers assess the similarity of the smells as well. They were interested to find that, indeed, the friends’ odors were more similar to each other than those of strangers. That could mean that odor was one of the things they picked up on as their relationship began.

“It’s very probable that at least some of them were using perfumes when they met,” Ms. Ravreby speculated. “But it did not mask whatever they had in common.”

However, there are many reasons friends might smell alike — eating at the same restaurants, having a similar lifestyle and so on — making it difficult to say if the smell or the basis for the relationship came first. To probe this, the researchers had 132 strangers, all of whom stank up a T-shirt first, come into the lab to play a mirroring game. Pairs of subjects stood close to each other and had to mimic the motions of the other as they moved. Afterward, they filled out questionnaires about whether they felt a connection with their partners.

The similarities of their odors, strikingly, predicted whether both felt there had been a positive connection 71 percent of the time. That finding implies that sniffing an odor similar to our own generates good feelings. It may be one thing we pick up on when we meet new people, along with things like where they grew up and if they prefer science fiction or sports. But Dr. Sobel cautions that, if this is the case, it is just one factor among many.

The Covid pandemic has so far curtailed further research using this design by Ms. Ravreby and colleagues; experiments in which strangers get close enough to smell each other have been difficult to set up.

But now, the team is looking into modifying people’s body odor to see whether subjects who’ve been made to smell similarly band together. If scent correlates with their behavior, that’s more evidence that, like other terrestrial mammals, we may be drawing on our sense of smell to help us make decisions.

There are many mysteries for them and other researchers to study about how our personal fragrances, in all their complexity, interact with our personal lives. Each puff of air may say more than you know.

“If you think of the bouquet that is body odor, it’s 6,000 molecules at least,” Dr. Sobel said. “There are 6,000 that we know of already — it’s probably way more.”