After Shaking Hands With People We Like To Sniff Our Hands: Thanks, Chemosignals

Sniff Sniff
Following a handshake, all of us unconsciously sniff our hands to pick up chemical messages left from the other person's sweat. Search Engine People Blog, CC BY 2.0

Anyone who’s ever seen two dogs interacting with each other knows they love sniffing each other’s butts. Why? Because their powerful noses are able to pick up loads of information, including the other dog’s gender, diet, and emotional state. Dogs aren’t the only ones to behave this way; rats and primates do as well, including humans, according to a new study. And when it comes to the way we do it, you may have never even noticed it.

The study, from researchers at the Weizmann Institute of Science in Israel, found that many of us sniff our hands after a handshake, and suggested it could be because we’re checking out their scents. In fact, they found the average number of seconds a person spent smelling their hands nearly doubled after shaking another person’s hand when compared to smelling their own hand for the sake of it.

“It’s well known that germs can be passed on through skin contact in handshakes, but we’ve shown that potential chemical messages, known as chemosignals, can be passed on in the same manner,” said Idan Frumin, a research student at the Institute, in a press release. It’s hard to believe that our hands would unconsciously move up to our noses for a sniff following a handshake (we’re just scratching our noses, right?), but whether it was immediately after or once that person left the room, sniffing increased by over 100 percent.

The researchers conducted their study first by donning latex gloves and shaking the hands of 271 participants in order to pick up their unique odors. They found all of the participants left behind the chemicals squalene, geranyl acetone, and hexadecanoic acid, all of which are chemosignals released by insects, dogs, rats, and other mammals.

Once they had confirmed we all release these chemosignals in our hands’ sweat, they performed several experiments on the participants, all of whom were hooked up to instruments meant to measure airflow through their noses. Participants were left alone in a room for a short period of time before a researcher came in; only some of them shook hands. They found that the participants who shook hands were more likely to sniff them once the researcher left than those who didn’t; for example, “by touching their nose,” the study said.  

But interestingly, the hand they sniffed depended on whether the researcher was a man or a woman. Those who shook hands with someone of the same sex were more likely to sniff their right hand than those who shook hands with someone of the opposite sex — they were more likely to sniff their left hand. The researchers confirmed this wasn’t just some random coincidence by manipulating the scents passed on through the handshakes with perfumes or gender-specific odors. This time, the researchers found that when the scent was that from a man or woman, people were more likely to sniff their own hands, while they were less likely to do so when they shook a perfumed hand.

The findings add to a surprisingly diverse body of research on the use of chemosignaling in humans. Studies have shown women who breastfeed increase sexual desire through pheromones in women around them; smelling the tears of a woman who is crying reduces her sexual appeal; and smelling sweat produced from a person who was either fearful or disgusted induced such facial expressions.

Speaking to New Scientist, Noam Sobel, head of the Weizmann Institute’s Neurobiology Department, said, “I am convinced that this is just the tip of the iceberg. This is just one more instance where chemosignaling is a driving force in human behavior. When we were coding the videos, we would see people sniffing themselves just like rats. It’s like blind sight — you see it all the time but you just don’t think of it.”

Source: Frumin I, Perl O, Endevelt-Shapira Y, et al. A social chemosignaling function for human handshaking. eLife. 2015. 

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