Photo: WIN-Initiative

A word of caution: After reading this, your next handshaking experience is going to be weird. According to a team of Israeli researchers at the Weizmann Institute of Science, after shaking hands, many people covertly — and likely unconsciously — sniff their hands. In other words, humans literally sniff each other out upon meeting, much like animals do, writes lead author Idan Frumin and a research team in a new paper published online this week in eLife, an open-access, peer-reviewed journal.

Frumin secretly filmed 153 study volunteers before and after a researcher greeted them, either with a handshake or without. Some of the participants had been outfitted with nasal cannulas, so the researchers could monitor airflow to see whether they were sniffing or not.

Here’s how they describe what happened next:

After handshakes within gender, subjects increased sniffing of their own right shaking hand by more than 100%. In contrast, after handshakes across gender, subjects increased sniffing of their own left non-shaking hand by more than 100%.

And here’s the research team’s video of the post-handshake hand-sniffing, in case you were curious:

It’s not clear from these findings what might explain the gender disparity. As for what, exactly, the participants were smelling — some of the volunteers shook hands with a researcher who was wearing a latex glove, and a chemical analysis suggested that the gloves had picked up several chemicals that are considered to be important in social signaling among some animals, and possibly humans, too.

All of this sounds incredibly bizarre — okay, it is pretty bizarre — but New Scientist points out that preexisting research has already identified some of the ways people use scent to unconsciously communicate. Noam Sobel, a co-author on this paper, led a different study that showed men become less sexually aroused after smelling women’s tears. (When asked to explain the reason behind this apparent cause-and-effect, Sobel told New Scientist in 2011, “We’ve identified a word that means ‘no’ in the language of chemical communication. We know that women tend to cry more during menstruation, when it’s not an effective time to conceive.”)

Figuring out exactly what — and why — you may be communicating via scent with a handshake requires further research; a more immediate impact of this finding is to drastically increase the awkwardness of your next handshake, as you can’t help but watch for the subsequent sniff.