It is said that happiness is contagious and now scientists believe they may know why.
For the first time researchers have found that humans can detect whether another person is feeling joyful by their scent.
They found that the odours produced by our bodies can communicate our happiness to others, a phenomenon known as chemosignalling.
Chemosignals act as a medium through which people can become "emotionally synchronised", outside of their conscious awareness.
Although chemosignalling had previously been shown to convey fear and disgust, little was known about how it related to positive emotions, the researchers from Utrecht University in the Netherlands said.
For their study, they collected the sweat of "sender" participants in happy, fearful and neutral states using pads placed under their armpits while they watched different film clips. These pads were cut up, put into jars, and presented to a group of "receivers" to sniff, in a random order.
While they sniffed, the testers were hooked up to an electromyograph, which measured subtle differences in the activity of their facial muscles as a function of the emotion they were experiencing.
"Exposure to sweat from happy senders elicited a happier facial expression than did sweat from fearful or neutral senders," the researchers wrote in the journal Psychological Science.
"Our findings suggest that not only a negative state, but also a positive state (happiness) can be transferred by means of odours."
The researchers said: "Happiness benefits the individual on multiple levels, as it restores the damaging impact of negative emotions on the cardiovascular, neuroendocrine, and immune systems, and broadens attention to inspire creative ideas.
"Humans are a social species with the capacity to share these positive effects, using not only modalities such as vision, hearing, and touch, but also - as this exploratory study indicates - the sense of smell."
Earlier this month scientists discovered a chemical compound that can stimulate the areas of the brain responsible for releasing sex hormones in the brains of women.
Although it has long been debated whether humans can actually communicate via pheromones - the chemical signals secreted by animals to help find a mate - researchers have found that the scent of Hedione generates a activation pattern in the Nasal tissue of women which links to the brain.