According to experts, sweat people produce when they are scared gives off signals that are subconsciously picked up by others.
The finding by Stony Brook University in New York may explain why individuals with phobias such as a fear of flying can infect others who normally exhibit no such worries.
The study found people who are scared give off "pheromones" - hormones - that subconsciously trigger parts of the brain associated with fear, reports the Telegraph.
The boffins, who said it was too early to say whether the brain triggers actually resulted in people being scared, concluded that fear could be "contagious".
To reach the conclusion, U.S. researchers collected the sweat of novice skydivers - 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 skydive - 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.
The team, led by Lilianne Mujica-Parodi, told New Scientist magazine that their results "indicate that there may be a hidden biological component to human social dynamics, in which emotional stress is quite literally 'contagious"'.