People use handshakes to sniff each other out
Research shows that people unknowingly use the touch of a handshake to collect and sniff molecular signals from the other person.
Animals often sniff each other as a form of greeting to communicate with each other through chemical signals in their body odors. However, in humans this form of behavior is considered taboo, especially between strangers.
Scientists argue that, in spite of our efforts to avoid being ‘smelly’, we may actually smell each other without being aware that we do so. Now, Idan Frumin and co-workers first put on latex gloves and then shook hands with volunteers to collect samples of their odor. Chemical analysis of the gloves found that a handshake alone was sufficient to transfer the volunteers’ odor. These odors were made of chemicals that are similar to ones that animals smell when sniffing each other.
Therefore, when we shake hands with a stranger, it is possible that we may inadvertently smell the stranger’s chemical signals. To address this possibility, Frumin and co-workers investigated how humans behave after shaking hands with a stranger. Volunteers were asked to wait in a room alone before they were greeted by one of the researchers. Some of these volunteers were greeted with a handshake and others were greeted without a handshake. Afterwards, all the volunteers spent some time in a room by themselves where their behavior was covertly monitored.
Frumin and co-workers found that volunteers who shook hands were more likely to sniff their hand, for example, by touching their nose when they were in the room on their own, than those who did not shake hands. After the volunteers shook hands with someone of their own gender, they spent more time sniffing their right hand (the one they had used for the handshake). However, after the volunteers shook hands with someone of the opposite gender, they spent more time sniffing their left hand instead.
Next, the body odor of some of the experimenters was tainted by perfumes or gender-specific odors. Volunteers who shook hands with these tainted individuals behaved differently; when the experimenter was tainted with perfume the volunteers spent more time sniffing their own hands, but when the experimenter was tainted with a gender-specific odor they spent less time sniffing of their own hands. This shows that different smells influenced the hand sniffing behavior of the volunteers.
Frumin and co-workers’s findings suggest that a simple handshake may help us to detect chemical signals from other people. Depending on the person’s gender, we may respond by sniffing our right hand to check out the person’s odor, or our left hand to smell ourselves in comparison. Future studies will involve finding out how this sniffing behavior could work as an unconcious form of human communication.
To find out more
Listen to Idan Frumin discuss handshakes in episode 18 of the eLife podcast.
Read the eLife research paper on which this story is based: “A social chemosignaling function for human handshaking” (March 3, 2015).
Read a commentary on this research paper: “Social chemosignaling: The scent of a handshake”.
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
