New research suggests that anxiety triggers the release of a scent that causes other humans who smell it to empathize with you. This may have evolved to help speed up spread of fear within a population so groups can get away quickly from dangerous situations. To run the experiment, University of Dusseldorf psychologist Bettina Pause and her colleagues had students undergoing brain scans sniff absorbent pads taken from the armpits of other students just before a final exam and, separately, while they were exercising. Pleasant.
None (of the sniffing students) perceived a difference between the two types of sweat, but the pre-exam sweat had a different effect on brain activity, lighting up areas that process social and emotional signals, as well as several areas thought to be involved in empathy...Fellow students smell your exam fear
A previous experiment found that sweat from skydivers activated anxiety circuits in sniffers' brains.