It turns out, our brains are quite finely tuned to detecting illness in others. New research suggests that subtle facial cues alert us to infections mere hours after they take hold.

This research could one day help train AI systems to detect illness as well. A study published in the journal Proceedings of the Royal Society B took 16 healthy volunteers and injected them, at different times, with both a placebo and a type of E. coli bacteria that causes flu-like symptoms. The volunteers, who did not know which injection they had just received, were photographed two hours after each shot.

These photographs were then shown to 62 participants who were asked to judge whether the person in the picture was healthy or sick. These participants had to make the judgement after only viewing the photo for five seconds.

The participants were only able to detect a sick person 52 percent of the time, hardly better than chance. But they were able to detect a healthy person 70 percent of the time.

Facial features related to judgements of sickness included redder eyes, duller skin, a more swollen face, a droopier mouth and eyelids and paler skin and lips. The sick photos were also rated as looking more tired. Read more from smithsonianmag.com…

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