How can you tell if someone is happy? Most of us would say by looking at the smile, listening to the laughter or seeing that unmistakable twinkle in the eye. While these are all true measures of a happy disposition, we also tell if others are happy in a much less obvious way: their scent. And we’re not talking about their choice of perfume or cologne. We mean their sweat. European researchers have demonstrated — at least in the lab — that human beings pick up on others’ positive emotions via chemicals secreted in their sweat, reports HealthDay News. And this actually makes sense, since previous research has shown that negative emotions, such as fear or disgust, can be communicated by human scent. When we breathe in that scent of happiness in someone else, it makes us happier, too. The study found that when the women sniffed the “happy sweat,” their faces also showed happiness, something the researchers called behavioral synchronization. That is, the sweating man’s emotional state was picked up by the women and revealed in their facial muscles.