Humans can smell fear, detecting molecules in sweat odour which indicate another person is afraid, according to German psychologists.
Previously it was thought that only animals such as fish, flies and rodents had such a faculty.
But the detection in humans is unconscious.
"We are the first in the world to prove that emotions can be communicated chemically between humans," said Bettina Pause, a psychology professor at the University of Dusseldorf who led the study.
They team showed that when a person smells "fear" molecules from somebody else's skin, this stimulates regions of the brain responsible for empathy and interpreting other people's emotions.
Pause said humans know someone else is afraid without knowing how they know.
How the study was done
The 10-year-long study used swabs of "cold sweat" taken from the armpits of 50 students while they were sitting examinations and were scared of failure.
The odour was wafted into the noses of 28 people connected to brain scanners, only half of whom said they could even smell sweat, yet their brains responded.
"It means that when humans detect fear by smell, they feel similarly and it triggers empathy," said Pause, who believes the faculty mainly helps humans sense danger, for example by knowing when strangers are nervous.
But so far the "smell of fear" has not been isolated.
"We think these they are volatile molecules that easily travel a certain distance," Pause said, adding that antiperspirants cannot really hide it if you are afraid.
"Deodorants only block the signal for a short time," she said.
Causes of sinusitis