Humans subconsciously form friendships based on body odour - Study

Just when we thought that how we connect with others is solely based on vibe, character and things we love, new research has revealed that some make friends with people who smell the same as them.

The Weizmann Institute of Science researchers were able to predict the quality of social interactions between complete strangers by first "smelling" them with a device known as an electronic nose, or eNose.

These findings, published recently in Science Advances, suggest that the sense of smell may play a larger role in human social interactions than previously thought. Is that true?

Anyone who has ever walked a dog knows that their canine can usually tell from a distance whether an approaching dog is a friend or an enemy.

When in doubt, the dogs might sniff each other before deciding whether to plunge into a play session or an all-out war.

This dominant role played by the sense of smell in social interactions has been extensively documented in all land mammals except humans.

 Is this because humans do not use their noses in social settings the way all other terrestrial mammals do? Or is this behaviour covert, rather than overt, in humans?

A Graduate student Inbal Ravreby, in Prof. Noam Sobel's laboratory in Weizmann's Brain Sciences Department, hypothesized that the latter is the case.

She relied on two previous observations.

• First, she suggested that humans are constantly, although mostly subconsciously, sniffing themselves.
• Second, humans often subconsciously sniff other people. In addition, it's known that people tend to become friends with others who are similar to themselves in appearance, background, values and even in measures such as brain activity.

Ravreby hypothesized that when subconsciously sniffing themselves and others, people may be making subliminal comparisons and that they may then gravitate toward those whose smell is similar to their own.

Tests and results

To test her hypothesis, Ravreby recruited pairs of click friends based on same-sex nonromantic friends whose friendships had originally formed very rapidly.

She hypothesized that because such friendships emerge prior to an in-depth acquaintance, they may be particularly influenced by physiological traits such as body odour.

She then collected body odour samples from these click friends and conducted two sets of experiments to compare the samples with those collected from random pairs of individuals.

In one set of experiments, she performed the comparison using the eNose, which assessed the chemical signatures of the odours. Then in the other, she asked volunteers to smell the two groups of body odour samples.

In both types of experiments, she found that click friends were found to smell significantly more like each other than did the individuals in the random pairs.

Limitations and findings

What if the friends had a similar smell because they ate the same types of food or shared other life experiences that influence body odour?

Next, she wanted to rule out the possibility that body odour similarity was a consequence of click friendships, rather than a contributing cause.

To address this issue, Ravreby used an eNose to "smell" a number of volunteers who were complete strangers to one another and then asked them to engage in nonverbal social interactions in pairs.

To collect body odour the participants were told to avoid all perfumes and scents while sleeping in a cotton T-shirt for two nights.

After each such structured interaction, the participants rated the other individual in terms of how much they liked that person and how likely they were to become friends.

After analysis, it was revealed that the individuals who had more positive interactions indeed smelled more like each other, as determined by the electronic Nose.

In fact, when Ravreby and statistician  Kobi Snitz entered the data into a computational model, they were able to predict with 71 percent accuracy which two individuals would have a positive social interaction, based on eNose data alone.

In other words, body odour appears to contain information that can predict the quality of social interactions between strangers.

Last words

"These results imply that, as the saying goes, there is chemistry in social chemistry," Ravreby said.

"This is not to say that we act like goats or shrews. Humans likely rely on other, far more dominant cues in their social decision-making. Nevertheless, our study's results do suggest that our nose plays a bigger role than previously thought in our choice of friends." Prof. Noam Sobel, head of the Azrieli National Institute for Human Brain Imaging and Research said.

A couple of fascinating recent studies have also found that emotional states in humans can be communicated through body odors.

The new study was published in the journal Science Advances.