What's in a handshake?

We all do it, there's no denying it. You reach out, take a firm grip and shake vigorously while trying to look the other person in the eye and look confident. But then comes the part that no one had previously noticed, until Israel's Weizmann Institute research Idan Frumin began secretly filming people greeting one another in his research lab... 

"People sniff their fingers after they shake someone's hand," he explains. "We're doing the more socially acceptable human equivalent of what two dogs do when they meet one another!"

To conduct the research, published in the journal eLife, Frumin and his colleagues invited volunteers to take part in a study but didn't initially tell them what would be happening. He arranged for one of the research team to greet participants in a waiting area, either with or without a handshake. The interaction was filmed on hidden cameras, together with the ensuing two minutes of activity following the initial greeting.

The researchers were looking at the footage specifically to see what the subjects did with their hands. "After a handshake, the subjects' right hands - the one that was shaken - spent significantly longer in the vicinity of the nose compared with before the handshake."

To prove that the subjects were genuinely sniffing their shaken fingers, Frumin also rigged up a test to monitor nasal inhalation in a group of subjects. "As the fingers came near the nose they inhaled, showing that a sniff had taken place!"

The team speculate that, by bringing our hands to our noses in this way, we're sampling the scent profile of the person we are greeting in much the same way that other animals give each other a nasal probing.

"We know that chemicals are being transferred between shaken hands because we asked an experimenter to wear a glove and shake some hands. A sensitive analyser could detect the transfer of a range of chemicals between the shaken hand and the glove,"  explains Frumin.

So next time someone shakes your hand, watch for the surreptitious finger sniff that comes shortly afterwards...