Does your nose help choose your friends?

Human beings maintain the polite fiction that we don’t constantly feel for each other. Despite our best efforts, we all have our own smells, pleasant and less pleasant, and if we are like other land mammals, our particular scent could mean something to our fellow human beings.

Some of them, like the stench of someone who hasn’t bathed in all month, or the characteristic smell of a toddler claiming he didn’t just fill his diaper, are self-explanatory. But scientists who study human olfaction, or your sense of smell, wonder if molecules emanating from our skin can register at a subconscious level in the noses and brains of people around us. Do they carry messages that we use in decisions without realizing it? Could they even shape who we like and dislike to hang out with?

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

Many factors determine who people become friends with, including how, when, and where we meet someone new. But maybe one thing we pick up on, the researchers suggest, is their smell.

Scientists studying friendship have found that friends have more in common than strangers – not just things like age and hobbies, but also genetics, brain activity patterns and appearance. Inbal Ravreby, a graduate student in the lab of Noam Sobel, an olfactory researcher at the Weizmann Institute of Science in Israel, was curious if particularly fast friendships, those that seem to form in an instant, had an olfactory component – if people could pick out similarities in their smells.

She recruited 20 pairs of so-called click friends, both of whom characterized their friendship this way. Then she put them on a diet common in human body odor research: stop eating foods like onions and garlic, which affect body odor, for a few days. Eliminate aftershave and deodorant. Bathe with unscented soap provided by the laboratory. Then put on a fresh, clean t-shirt provided by the lab and sleep in it to get good and smelly, before handing it over to the scientists for examination.

Ms Ravreby and her colleagues used an electronic nose to assess the volatiles coming from each t-shirt, and they also asked 25 other volunteers to rate the similarity of the smells. They were interested to note that indeed, the smells of friends resembled each other more than those of strangers. It could mean that the smell was one of the things they noticed early in their relationship.

“It’s very likely that at least some of them were using perfumes when they met,” Ms Ravreby speculated. “But that didn’t hide everything they had in common.”

However, there are many reasons why friends may feel the same – eating at the same restaurants, having a similar lifestyle, etc. – making it hard to tell if the smell or the base of the relationship came first. To probe this, the researchers brought 132 strangers into the lab, all of whom might stink of a t-shirt, to play a mirror game. Pairs of subjects stood close together and had to mimic each other’s movements as they moved. Then they filled out questionnaires to find out if they felt a connection with their partners.

The similarities in their smells, strikingly, predicted whether the two felt there had been a positive connection 71% of the time. This discovery implies that sniffing a smell similar to ours generates good feelings. Maybe it’s something we remember when we meet new people, as well as things like where they grew up and whether they prefer sci-fi or sports. But Dr. Sobel warns that if this is the case, it is only one factor among many.

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

But now the team is looking to alter people’s body odor to see if subjects who were tricked into smelling the same way unite. If smell correlates with their behavior, it’s further proof that, like other land mammals, we can rely 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 scents, in all their complexity, interact with our personal lives. Every puff of air can say more than you think.

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


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