The old saying goes that happiness is contagious. New research suggests there might actually be some science to back that up. Happiness, scientists say, has a distinct smell that humans can sense on one another. And when we get a good whiff of someone else's joy, we get happier too. 

The key lies in our sweat. According to psychological scientist Gün Semin of Utrecht University in the Netherlands, senior research on the study, "[B]eing exposed to sweat produced under happiness induces a simulacrum of happiness in receivers, and induces a contagion of the emotional state." 

He and his team collected sweat samples from a group of 12 men as they watched videos meant to induce different emotions, like happiness and fear. The sweat samples were then passed along to a group of female test subjects for sniffing.

The researchers wanted to know how the different sweat samples made women feel. To measure this, they watched for changes in facial expression that might indicate an emotional response. When women were exposed to “happy sweat,” their faces displayed classic microexpressions associated with pleasure: the muscles around their eyes activated as if they were about to flash a genuine, happiness-induced grin. This is called the “Duchenne smile,” and it’s a giveaway sign of true joy. The man who discovered it, French anatomist Guillaume-Benjamin-Amand Duchenne de Boulogne, once said, "The muscle around the eye ... is only brought into play by a true feeling, an agreeable emotion. Its inertia in smiling unmasks a false friend."

We already knew that chemicals in our sweat can convey fear. When we “smell” fear on someone else, the stress centers in our brains are activated and we become more alert, ready to defend ourselves from a threat. That's evolutionarily useful.

Pamela Dalton, an olfactory scientist at the Monell Chemical Senses Center in Philadelphia, says the communication of danger-induced fear is so important that she "would expect the ability to communicate a happy emotion to [actually] be less potent than the ability to transmit a negative emotion." But that may not be the case.

The findings could have big implications for how we treat depression or mood disorders. “If we can actually extract the biochemical combination that is induced by happiness, then you can have products that are ‘laced’ with this biochemical and will make people feel more positive,” Semin says

More research is needed before we can put happy spray in a can. “Researchers would have to parse out its unique chemical cocktail from among the 180 to 200 known chemicals that make up human body odor,” writes Rachel E. Gross at Slate. “That’d be like determining Coca-Cola’s proprietary formula from scratch.” Also, the study only looked at how sweat influences women. The researchers claim this is because “women generally have both a better sense of smell and a greater sensitivity to emotional signals than men do.” But we’d need to know if the effect exists for men, as well. 

Finally, while this study is fascinating, it should be taken with a big grain of salt until the findings can be replicated. Why? It was funded in part by Unilever, which sells—you guessed it—Axe body spray.