Apparently, the mere sight of a sick person can send your immune system into overdrive. In a fascinating new study, researchers asked a group of young adults to watch a slideshow of images showing people with all sorts of illnesses. They took blood samples from the subjects before and after the experience, and introduced a strain of bacteria to each. The “after” samples produced much more IL-6, indicating a more aggressive immunological response, Psychology Today reports.
“It makes enormous evolutionary sense,” gushes one study author. “Here’s one way to think about it: Immunological responses sure are useful, but they come at a cost (Inflammation ain’t fun, and IL-6 doesn’t grow on trees.)” So your immune system only responds aggressively when it believes the threat of infection is high—and it uses visual clues to decide that. “If you see a bunch of people around you who look sick, that’s a pretty good indicator that you’re in imminent danger of infection.”