Sniff You Later: Handshakes Are Based On This Ancient, Smelly Custom

A formal greeting today typically involves shaking hands. Hugging is usually reserved as a more informal hello between close friends. Yet did you know a handshake goes way back? It's actually part of an ancient custom that involved sniffing out an acquaintance's odor that rubbed off on your hand. 

New findings published in the journal eLife show that within just a number of seconds study subjects spent sniffing their own right hand more than doubled when an experimenter greeted them with a handshake.

"Our findings suggest that people are not just passively exposed to socially-significant chemical signals, but actively seek them out," said Idan Frumin, the research student who conducted the study under the guidance of Prof. Noam Sobel of Weizmann's Neurobiology Department, in a news release. "Rodents, dogs and other mammals commonly sniff themselves, and they sniff one another in social interactions, and it seems that in the course of evolution, humans have retained this practice -- only on a subliminal level."

Researchers had experimenters wear gloves when they first shook hands to see if handshakes transferred body odors. The other subjects did not have on gloves and were tested for small residues. They found that a handshake alone was sufficient for the transfer of several odors known to serve as meaningful chemical signals in mammals.

Then, they looked to see how odors communicate with each other. Scientists used covert cameras to film 280 volunteers both before and after they were greeted by an experimenter who either shook their hand or didn't.

Researchers found that after shaking hands with an experimenter of the same gender, subjects more than doubled the time they later spent sniffing their own right hand--the hand they shook with. However, after shaking hands with an experimenter of the opposite gender, the subjects increased the sniffing of their own left hand (the non-shaking one).

Another series of tests were then performed to make sure that the hand-sniffing was related to checking odors and not just stress-related. Nasal air-flow was measured, showing that subjects were actually sniffing their hands, confirming the olfactory nature via the hand-sniffing.

"Handshakes vary in strength, duration and posture, so they convey social information of various sorts," concluded Prof. Sobel. "But our findings suggest that at its evolutionary origins, handshaking might have also served to convey odor signals, and such signaling may still be a meaningful, albeit subliminal, component of this custom."

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