It’s a rare intersection, being both sweaty and in a good mood. Usually the only context where the marriage occurs is at the gym, right after a hard-fought workout. But assuming you can bear the added moisture during other parts of your day, science now says the sweat coming through your pores is making your happiness contagious.

Olfactory communication — that is, your sense of smell — was likely the first sensory system that evolved, says Gün Semin, professor of psychology at Utrecht University, in the Netherlands. Early humans needed a way to make quick decisions to ensure their survival, so it was in their interest to develop a link between their physiological responses and their brain’s executive commands, such as Run.

“Fear sweat induces a state of alertness,” Semin told Medical Daily, and it “enhances the visual field that is attended to.” These forms of communication are collectively known as chemosignals, and they formed the basis of Semin’s latest study into emotional contagions.

He and his colleagues devised an experiment whose purpose was to find out how well the chemosignals in sweat transferred to other people. They brought in 12 men to their lab, none of whom smoked, took any medications, or suffered from any psychological disorders. The men took off their shirts, wiped down their armpits until they were dry, and sat down to perform two tasks. The first was watching a video that was intended to elicit either a neutral response, a fear response, or a happiness response. Then they completed an assessment of their implicit emotions, based on their feelings toward certain Japanese symbols. At the end of both tasks, the scientists removed the pads and collected the sweat in vials.

Next, 36 women visited the lab. (Semin’s team chose an all-female cast because women are generally more sensitive to smells and reading emotion.) Each woman rested her chin on a chin rest and proceeded to sniff vial after vial of sweat, taking five-minute breaks between each one. Meanwhile, Semin and his team were tracking the movement of the women’s facial muscles so that later they could crosscheck the perceived emotion with the emotional state of the man at the time he produced the sweat.

They found striking parallels between how the women reacted and which emotional group the men had belonged to. Women produced the early signs of a genuine smile, such as squinted eyes and raised cheeks, when they smelled the happiness group, while the women who smelled the fear sweat produced more activity in their frontalis muscle, the one that blankets your forehead and permits eyebrow-raising.

“The facial muscles activated in a happy state are distinctly different ones from a fear or neutral state,” Semin said, “and we find that when people inhale a happiness odor, then the distinctive facial muscles that are activated during a genuine smile, are activated.”

An important detail of the study is that emotions weren’t being consciously perceived. When the researchers asked the women how pleasant and intense each vial was, their answers didn’t line up with the data revealed by their facial muscles. According to Semin, this isn’t entirely surprising. The information our brains attend to isn’t necessarily getting communicated to us explicitly. Often, it’s not. Audio and visual cues, for instance, both have a relationship to implicit emotions that is similar to olfactory communication, “but not an interactive one.”

Semin says future research is needed to untangle what is actually doing the heavy lifting in the interplay between odor and emotions. For example, the camaraderie of a 5K race may very well be what’s getting people to cheer each other on, but it could also just be their sweat talking.

Source: De Groot J, Smeets M, Rowson, et al. A Sniff of Happiness. Psychological Science. 2015.