The underlying purpose for shaking hands may be to get a whiff of people, according to a paper published on Wednesday by a team of researchers in Israel.

Prof. Noam Sobel, chairman of Neurobiology at the Weizmann Institute, found people showed a tendency to sniff their hands after shaking the hand of a person they have just met, suggesting that the grip is a way of transferring social chemicals.

“It is well-known that we emit odors that influence the behavior and perception of others but, unlike other mammals, we don’t sample those odors from each other overtly,” Sobel said. “Instead, our experiments reveal handshakes as a discreet way to actively search for social chemo-signals.”

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In a series of experiments, some 270 participants were covertly filmed as they each greeted one of a variety of researchers, with or without a handshake.

Researchers discovered that 22 percent of the time, both men and women had their hands near their noses to get a whiff of themselves, even before the meet and greet. However, after greeting the researcher, that behavior doubled. As the researcher left the room people sniffed their right hands twice as much as they did before the shake.

Curiously, when shaking with a member of the opposite sex left-hand smelling doubled, possibly to reassure the shakers of their own smell by comparison, Sobel speculated.

“We tend to think of social chemo-signalling as a cross-gender story but it’s not,” Sobel said according to a report from New Scientist. “There are plenty of instances where signalling happens within the same sex such as women synchronizing their menstrual cycles or rodents sniffing out dominance.”

Some of the participants were fitted with nasal monitors that confirmed they were smelling their hands when they brought them up to their nose. The volume of air inhaled increases when the subject is smelling rather than simply breathing.

Researchers also wore sterile gloves some of the time in order to sample what chemicals might be transferred from hand to hand. The results showed that squalene and hexadecanoic were present, both of which are known to be used as chemical signals among dogs and rats.

“This is just one more instance where chemo-signalling is a driving force in human behavior,” Sobel said. He noted that the frequency of hand-sniffing was a surprise.

“When we were coding the videos we would see people sniffing themselves just like rats,” he said. “It’s like blindsight – you see it all the time but you just don’t think of it.”

The research paper was published online on the eLife website.

Handshaking has a long history. A 5th century BCE Greek funeral stele shows two soldiers and a priest shaking hands, but the exact origin of the widely recognized greeting is a mystery.

Most previous theories revolved around it being a gesture of peace by showing that the hand doesn’t hold a concealed weapon.