“Bosom Friends” have something in common: their smell

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(ORDO NEWS) — Have you ever met a complete stranger and felt like you “got it together” almost immediately? Now, this feeling of “chemistry” can actually be chemistry.

Twenty pairs of same-sex platonic friends took part in an Israeli study and said they had a feeling of sympathy upon meeting.

Using an electronic nose (and volunteers who heroically agreed to sniff T-shirts worn at night), the researchers concluded that pairs of friends smell more similar than randomly paired strangers.

Many other mammals sniff each other to decide whether to play with an unfamiliar animal, attack or run away from it.

“In humans, the role of the sense of smell has been downplayed in part due to various social taboos, resulting in the perception that the sense of smell is of little importance to human sociality,” the researchers write in their paper.

But what if complete strangers “begin to interest us at the first sniff, and not at first sight?”, neuroscientists asked. After running several experiments to rule out alternative explanations, they concluded that “there is chemistry in social chemistry.”

In the main experiment, 20 pairs of friends were asked to wash with unscented soap, avoid foods like curry and garlic, and sleep in a separate bed from their partner.

They were instructed to wear a fresh cotton T-shirt every night for at least six hours and then place the T-shirt in a resealable plastic bag. The T-shirts were then frozen and thawed one hour before the sniffing experiments began.

Body odor samples were passed through a compact PEN3 eNose gas sensing device, which contains a gas sampling unit and a sensor array. A simple plotting method was then used to determine the similarity between odors, comparing five different sensor responses.

In another test, 25 sniffers were recruited to compare scents using a T-shirt sniffer (a glass jar with a T-shirt inside, connected to a mask that ensures no other smells interfere with the test).

The sniffers examined two scent samples at a time, some from random pairs of people and others from friends who snapped each other.

In this experiment, both volunteers and eNose found more similarities between friends than between strangers.

However, not all experiments gave such clear results. When 24 volunteers compared three odor samples – two from friends and one from a stranger – they were unable to identify friendships as easily as those who compared only two samples.

“We think the task was too difficult,” says neuroscience graduate student Inbal Ravrebi, lead author of the paper.

Volunteers were also asked to rate 40 body odors from couples of friends on pleasantness, intensity, sex appeal, competence, and personality warmth.

When the researchers combined all five ratings, it turned out that the couples who interacted were rated as more similar than random couples.

And the research didn’t end there. The team also wanted to test if they could use the similarity of smells between complete strangers to predict whether they would look alike when they first met.

To do this, they recruited volunteers who had never met before and asked them to play a silent “mirror game” in which participants try to copy each other’s hand movements at close range for two minutes without talking.

The researchers ran this experiment in a circle, creating 66 different pairs; a third of couples said they were dating their partner. After odor samples were run through the eNose instrument, pairs that bonded were found to have significantly more chemical similarity than pairs that did not bond.

“I think this is the strongest result because it shows that we can predict clicks with 71 percent accuracy,” Ravrebi told ScienceAlert.

Previous research has shown that the smell of a stranger activates the amygdala, the fear center in the brain, while the smell of a friend does not.

We also know that people born without the sense of smell are often at a disadvantage in many social situations because of their condition; at the same time, people with autism spectrum disorder (ASD) have altered social chemosignaling.

(In one study, people without ASD responded to skydiver sweat by becoming more alert, while those with ASD did the opposite.)

COVID-19 causes a long-term loss of smell in a very small proportion of people. It’s hard to say what impact this might have on social interaction, Ravreby says.

“In many cases, it’s not complete anosmia, but partial anosmia, where people can distinguish some smells but not others,” she says. “I would suggest body odor will continue to play a role.”


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