Stress can be "caught" from strangers, a team of psychologists from Saint Louis University claims.
Their groundbreaking study shows that in some situations stress is contagious.
However, they say it can also lead to heroic behaviour in some people.
The team wanted to know how susceptible strangers were to "secondhand stress".
To test the theory, they took a group of participants and asked some to perform a public speaking or mental arithmetic challenge while the others observed.
The researchers measured the levels of cortisol and a stress-related salivary enzyme in the stressed speakers and the observers.
They found that the stress response in the witnesses was "proportional to that of their paired speakers and not influenced by gender".
Stress can be passed on through things like tone of voice, facial expressions, posture and even odour, the team say.
"We have demonstrated that stress can be contagiously caught from targets to observers," the researchers wrote.
"To find that in some people, some of the time, you can elicit these responses just by sitting and watching someone else under stress was somewhat surprising to us," Tony Buchanan, associate professor in the Department of Psychology at Saint Louis University, told ABC.
How the research happened
The team took a group of participants and asked some to perform a public speaking or mental arithmetic challenge while the others observed.
The researchers measured the levels of cortisol and a stress-related salivary enzyme in the stressed speakers and the observers.
They found that the stress response in the witnesses was "proportional to that of their paired speakers and not influenced by gender".
Stress can be passed on through things like tone of voice, facial expressions, posture and even odour, the team say.
- Daily Mail