Researchers at the Weizmann Institute of Science in Rehovot, Israel secretly videoed 153 volunteers to see if they sniffed their hands after shaking 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.