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June 24 (UPI) -- The nose knows when it comes to sniffing out same-sex friends, new research suggests. The study, published Friday in Science Advances, tested the hypothesis that body odor contributes to bonding in pairs of same-sex, non-romantic people.
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The bottom line? People with similar body odors are indeed likelier to become friends, according to the Israeli researchers.
"The gist is that people who 'click' with each other have similar body odor," Inbal Ravreby, a doctoral student in the department of brain science in Weizmann Institute of Science in Rehovot, told UPI. She is the study's lead author.
The scientists also found that pairs of established friends may smell more alike than random pairs of strangers.
And the researchers discovered that an electronic nose that maps odor similarities could predict which pairs of strangers would end up bonding during social interactions.
Researchers said they spent six months using social media to find 20 same-sex, non-romantic friends who mutually described their initial encounter as a "click" -- meaning that "a strong sense of bonding formed almost instantaneously between them."
Participants then "donated body odor using a strict body odor donation protocol," the research paper said.
The scientists observed that objective ratings obtained from an "electronic nose" converged with subjective ratings from 24 human "smellers" to suggest that "click-friends" smell more similar to each other than random pairings of people.
Ravreby said the electronic nose is "an analytical device made of sensors providing a representation of odor."
"In our electronic nose there are 10 metal oxidesensors, each coated with a different material conferring chemical specificity," she explained.
"Thus, each sample is potentially made of 10 responses that combine to generate a specific pattern associated with an odor. For our body odor samples, five sensors were activated."
Ravreby said the objective ratings obtained with an electronic nose are based on chemical similarity. By contrast, she said, "the ratings of humans are always subjective."
"To put it in other words, we mean chemical similarity and the perceived similarity (as humans perceived it)," she said, noting that the human smellers "were not trained in any way, so they may represent the ratings of the general, untrained, population."
Subsequently, the researchers said they found that they could use the electronic nose to predict which strangers would later form better paired interactions.
The scientists recruited complete strangers, "smelled them with an electronic nose, and engaged them in nonverbal same-sex dyadic [paired] interactions."
Ravreby said that all the participants who played the so-called "Mirror Game" first donated their body odor, "so we tested how similar the body odor of each dyad [pair] was."
When playing the game, the participants stood "half a meter apart and to move their hands as coordinately as possible without speaking," she said.
"This short distance enabled them to smell each other, mostly subconsciously, as happens also in a daily conversation," Ravreby said.
After each game the participants indicated whether they "clicked" and "also rated 13 aspects regarding the social interaction quality, such as liking, feeling of understanding the other, feeling that there was chemistry between them and whether they could be friends," she said.
"We found that by chemical body odor similarity as indicated by the electronic nose, we could predict clicking [with] 71% accuracy" among the paired participants, Ravreby said.
She added that the more similar the body odors were, the more the partners in the mirror game "liked each other, understood each other, felt there was chemistry between them and that they could be friends."
"More broadly, in 10 out of 13 ratings we found a relationship with body odor similarity such that the [more] similar the body odor, the better the quality of the interaction," Ravreby said, allowing the researchers to predict "clicking" and future quality of social interaction by chemical body odor similarity.
Ravreby said the research findings "suggest that body odor similarity influences our tendency to approach or avoid someone. Accordingly, loss of smell may mean also loss of important social information that influences our social behavior."
Ravreby said further research on the topic is planned.
"The next step is to manipulate humans' body odor and examine the underlying mechanism," she said.
"We will test whether when people smell someone with a similar smell to their own manipulated body odor, they would be more motivated to become friends than when smelling someone with a different body odor," she said.
She added: "This will be during a [functional] MRI scanning, which will enable us to examine whether indeed humans use their own body odor to compare to others' body odor.
"We hypothesize that when smelling a similar body odor, 'self' brain areas and 'social' brain areas will be activated more than when smelling different body odor."
