More to a handshake than meets the eye

The last time you greeted someone, did you shake their hand? Now a harder question - if you did shake hands, what did you do with your hand afterwards? You probably didn't realize it at the time but the likelihood is that you subconsciously brought it up to your face and sniffed your fingers. Using hidden cameras, Israel's Weizmann Institute researcher, Idan Frumin, has found that we humans effectively do the more socially acceptable equivalent of what two dogs do when they first meet.

Idan - People tend to sniff their own hands following a handshake. We first noticed that anecdotally. We just saw people do that after meeting new people and we set to find out if it's really something that we can describe as an effect. So, we devised a very simple experimental design that would allow us to film people without their knowing it and see if it is the case.

Chris - How did you actually do it then? Were you literally asking people to shake hands and then see what they did afterwards?

Idan - The design was very simple. We put people in a room without them knowing they are being filmed. After about 2 minutes, an experimenter went into the room and either shook or didn't shake their hands. The control, not shaking hands and the actual experiment was with shaking hands. We filmed them for an additional 2 minutes. We measured the time their hands spent near their noses, we focused on the right hand because this was the hand that was shaking but we also looked at the left hand which was not shaking. The results were a very substantial increase in the time that the right hand spent near the nose when there was a handshake.

Chris - Your interpretation of that would be that having shaken someone's hand, there's been a transfer of chemicals from the skin of one to the other. And therefore, if you give your hand a sniff, you're effectively sampling the chemical makeup, the chemical fingerprint, the odour profile of your opposite number.

Idan - Right. This is what we think and we also checked that. We actually measured if we can transfer chemicals from one person to another. We put gloves on an experimenter and shook their hands to see if something is left over from a handshake on this glove. And we saw that there are a host of chemicals that are transferred.

Chris - Is there evidence that when a person brings their hand to their nose they're actually sniffing their fingers? Could it not be that they're just rubbing their face or something?

Idan - This was one of our main concerns. To show that this is indeed something to do with the sense of smell, we measured that using a nasal cannula. It's basically a tube placed under the people's nose. We can measure the airflow using this instrument and we unequivocally saw that when their hand approached the nose, there is a great increase in airflow, meaning there was a sniff involved.

Chris - I don't know about you, Idan, but when I read your paper the first instinct I had was to immediately look down to see what I was doing with my hands and where they were. And I became conscious of every time after that I began to bring them close to my face. It's one of those awful things a bit like when you see someone yawn and you want to yawn, and someone says they're itching and you want to scratch. Are you now sort of obsessed with what you do with your hands?

Idan - Pretty much so, and I also observe that all the time. And it's very funny to see when we present that at conferences how people start to observe each other and themselves, and to see what they do with their hands after they shake hands. It's pretty amusing, yes.