Unlike dogs and other animals, humans — for the most part — don't sniff each other. Well, at least that's what we thought. A rather unsettling new study from the Weizmann Institute shows that practically all of us sniff our hands after handshaking — a possible sign of social chemosignaling behavior.

The new study, published in the journal eLife, suggests that humans use handshakes to exchange important chemical information — information that can alter our behavior is subtle ways. The researchers came to this conclusion by covertly filming 271 subjects as they they were being greeted in a structured event, some with a handshake and some without.

From New Scientist:

Before the greeting, both men and women had their hand near their nose 22 per cent of the time, on average. Airflow in the nose more than doubled at the same time, suggesting they were smelling their hands.

After shaking hands with someone of the same sex, on average volunteers sniffed their shaking hand more than twice as much as they did before the handshake. If the person was of the opposite sex, they smelled their non-shaking hand twice as much as before the handshake. This usually happened once the experimenter had left the room.

The team also carried out the experiment with people wearing sterile gloves. The chemicals the gloves picked up from the experimenter's hand included squalene and hexadecanoic acid, both of which are involved in social signalling among dogs and rats.

"People constantly have a hand at their face, they are sniffing it, and they modify that behaviour after shaking hands. That demonstrates that the handshaking is a chemosignalling behaviour," says [study co-author Noam] Sobel.

Whoa, that is weird. This study would appear to affirm the notion that social chemosignaling is not limited to opposite sex encounters. What's more, it suggests there may be other examples of chemosignaling that we aren't even aware of.

Thank you, science, for ruining every future handshake I'll have to make.

Check out more at New Scientist.