Hand sniffing after shaking hands is a real thing.

In the animal kingdom, scent acts like language. It's all about sending and receiving odors – the birds, bees, fish, and even rodents do it.

For humans, however... things have been less straightforward. The concept of 'chemosignaling,' which involves pheromones, is still debated.

This brings us to a research study by Israel's Weizmann Institute of Science, which suggests that humans indeed use their sense of smell to assess one another, especially during the often-overlooked aspect of an ancient social ritual: handshakes.

The study suggests that "Handshaking may serve as an active yet subconscious form of social chemosignaling," and it likely plays a significant role in human interactions.

The research examined 271 participants, observing their behavior after various structured events. Some participants shook hands, while others didn't. The findings show that hand sniffing is a fairly common behavior, especially after handshakes, which follow a certain pattern.

Here's a summary from the digest on eLife.org, where the study was published in 2015:

"The research revealed that participants who shook hands were more likely to sniff their hand (such as by touching their nose) when alone in a room, compared to those who didn't shake hands. After shaking hands with someone of the same gender, they spent more time sniffing their right hand (the one they had used to shake). However, after shaking hands with someone of the opposite gender, they focused more on sniffing their left hand."

This leads to the fundamental question posed by the study: Uh... why?

"Rodents, dogs, and other mammals often sniff themselves and one another in social settings. It appears that, over time, humans have kept this behavior — but on a more subconscious level," says Idan Frumin, one of the study's lead authors, in a Weizmann Institute press release.

Sharing scents within a species is a common practice. For instance, Fathead minnows use their urine to mark their territory. Ants, elephants, deer, and bees all rely on receptors to "smell" the chemical composition of others in their species.

This concept is widely accepted — unless, of course, you're human. Then, it becomes unclear. In a pivotal 2010 study, "The Great Pheromone Myth," Richard L. Doty, the director of the Smell and Taste Center at the University of Pennsylvania Medical Center, debunks the idea of a single chemical substance — pheromones — that transmits messages between humans.

One challenge is defining what a "pheromone" actually is. While many types exist, a general definition from biology-online states: "Chemical substances that, when released by an individual into the environment, cause specific reactions in other individuals, usually of the same species. These substances apply only to multicellular organisms."

However, some definitions are more rigorous. For example, in his book "Neurobiology of Chemical Communication," Doty argues that no chemical or combination of chemicals like that exists in humans: "Most definitions suggest that a pheromone (a) consists of one or a few chemicals, (b) is species-specific, (c) produces clear behavioral or endocrine effects, and (d) is minimally influenced by learning. To date, no chemicals have been identified in humans that meet these criteria."

Does this mean all the post-handshake hand-sniffing is pointless? Or that the research — another Weizmann Institute study — suggesting human tears contain a "chemosignal" is a hoax?

Not quite. It's clear that scents can influence people's moods, but the challenge lies in identifying the specific chemical agents (pheromones) responsible for these effects.

It seems that scientists and hand-shakers alike will continue to explore, trying to uncover the hidden messages in our scents.