AKA Olfactory Sampling
Non-human primates Mark Zuckerberg and Pope Francis shaking hands and about to smell each other's chemosignals once they start covertly raising their hands near their face in about 20 seconds from now.
After you shake someone's hand, you smell your own hand. Sometimes the shaking hand, and sometimes the opposite, depending on the gender match. They call it "olfactory sampling," but we call it "smelling your fingers," and despite its being in poor taste while in public view, we do it almost neurotically, albeit covertly -- so covertly that even we don't notice ourselves doing it.
I'm surprised this didn't resurface at the outset of the pandemic when we were all paying so much attention to how often we touch our face. In fact, the authors set us up thus:
Consistent with previous studies (Nicas and Best, 2008), we observed that humans often bring their hands to their noses. Of 153 subjects, 85 (55.55%) touched their nose with their hand at least once during baseline before the greet. Idle subjects had a hand (either right or left) at the vicinity of their nose for 22.14% of the time. (that's a lot of time!)
But this isn't just about how you can't keep your own hands off yourself:
Whereas facial self-touching has been considered a form of displacement stress response (Troisi, 2002), akin to rodent grooming, the novel framework we propose here for this behavior is that of olfactory sampling.
In this really carefully controlled study, they videotaped hundreds of people after shaking hands with a greeter at the lab, and even outfitted the subjects tubes near their nose to monitor their sniffing behavior. The results were "unequivocal," and remind us that we are in fact animals, sniffing up a storm:
We found that humans often sniff their own hands*, and selectively increase this behavior after handshake. 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%. Tainting participants with unnoticed odors significantly altered the effects, thus verifying their olfactory nature. Thus, handshaking may functionally serve active yet subliminal social chemosignaling, which likely plays a large role in ongoing human behavior.*For example, by touching their nose when they were in the room on their own; ... Criterion for scoring was any application of a hand to the face, as long as touching was under the eyebrows and above the chin; n=271 down to 153.
And later on in the report, things get even more complicated:
The body odor of some of the experimenters was tainted by perfumes or gender-specific odors. Volunteers who shook hands with these tainted individuals behaved differently; when the experimenter was tainted with perfume the volunteers spent more time sniffing their own hands, but when the experimenter was tainted with a gender-specific odor they spent less time sniffing of their own hands. This shows that different smells influenced the hand sniffing behavior of the volunteers.
Now that you know, you might notice yourself doing it constantly. What would be really interesting now would be to somehow get some anosmics up in the mix, maybe congenitally, maybe some recent long covid anosmics, and see how these numbers change?
Frumin I, et al. [incl Noam Sobel] A social chemosignaling function for human handshaking. eLife. 2015 Mar 03;4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4345842/