Contageous? Hormones in people's sweat could send invisible signals passing on their fear to others

veryone knows that an infectious giggle can spread through a room in an instant.

But scientists say that fear might be catching too – and that’s no laughing matter.

Research has shown that the sweat we produce when we are scared gives off signals that are subconsciously picked up by others.

Their experiments might explain why even those who normally fly with confidence, sometimes experience the occasional pang of doubt for no reason.

To investigate whether we can smell fear, U.S. researchers collected the sweat of novice sky-divers – and then asked others to sniff it.

First, the scientists taped absorbent pads to the armpits of 40 volunteers who were about to do their first sky-dive – and collected the sweat produced as they fell to earth.

Then a second group of men and women were asked to smell the samples – and some fear-free sweat – while having brain scans.

When ‘fear sweat’ was detected, the brain’s fear centres lit up more, New Scientist reports this week.

The researchers from Stony Brook University, in New York, said: ‘There may be a hidden biological component to human social dynamics, in which emotional stress, is quite literally, “contagious”.’

Previous experiments have shown it is possible to tell whether someone has watched a scary film or a comedy simply by smelling their sweat.

However, not everyone is convinced. Simon Wessely, who is a psychiatrist at King’s College London – and a health consultant to the Army, said past experiments have shown that chemicals alone cannot frighten us.

‘You can generate the physical symptoms of fear but people don’t necessarily get scared,’ he added.

Other critics refuse to accept that humans, like animals, are influenced by pheromones, chemicals transmitted through scent.

Meanwhile, some have concerns that studies such as the most recent, which was funded by the U.S. military’s research arm, could be used to develop ‘fear pheromones’ for military use.

It may not simply be fear that is coded in our sweat. Experiments have shown that body odour also plays an important role in the mating game.

Scientists believe that we seek out partners whose smell is different to our own. It is thought that the phenomenon evolved to prevent us unintentionally mating with relatives – or with those who are genetically similar to ourselves.

Even the smells associated with breastfeeding may harbour secrets. Research has shown that they raise the libido of other women.

These subtle smells are interpreted by the female body as a signal that the time is right to start trying for a baby, experts believe.