A new study says that, after a handshake, more than 1 in 5 people smell their hand. According to New Scientist:
The volunteers were filmed as they greeted a member of the team, either with or without a handshake. The researchers recorded how often the volunteers lifted their hands close to their nose, and how long they kept them there, the minute before and after the greeting. 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.