Humans Can Clock A Sick Person Just By Looking At Their Face

The biggest giveaways of the illness appeared to be pale skin, hanging eyelids, pale lips, and red eyes. Audrey Henderson/St Andrews University

It’s that time of year when everyone seems to be coughing, sneezing, or complaining they’ve got a sore throat. Fortunately, your brain has got your back.

New research published in the journal Proceedings of the Royal Society B has shown how humans are incredibly good at identifying whether people are suffering from an illness just by taking a glance at them. This heightened ability to detect infection is what is known as disease avoidance, a kind of “sixth sense” picked up through evolution to limit your chances of getting sick through a contagious lurgy.

"An ability to detect sick people would allow people to avoid being close to sick people, and hence minimise the risk of becoming sick if the person is a carrier of contagious disease," study co-author John Axelsson of Stockholm University told AFP.

The team of Swedish scientists tested this by taking took two sets of photographs of 16 healthy volunteers. First, they were administered with an injection of lipopolysaccharide, a molecule found on some pathogenic bacteria that provokes a strong immune response in animals. The molecules are sterile, so there was no chance of the person actually getting ill. After two hours they had their photograph taken, by which time their immune system had kicked in and essentially made them look under the weather.

For the second photograph the volunteers were unknowingly given a placebo injection, so were actually perfectly healthy. These two sets of photos were then shown to 62 other participants to see if they could tell the difference in the same person.

Can you spot the sick person? The face on the left shows a sick person and the right shows a healthy person. Audrey Henderson/St Andrews University

Observers were able to correctly spot a sick-looking person 81 percent of the time. The biggest giveaways of illness appeared to be pale skin, hanging eyelids, pale lips, and red eyes.

“This supports the notion that humans have the ability to detect signs of illness in an early phase after exposure to infectious stimuli. It would arguably be particularly beneficial to identify sick individuals at an early stage of sickness when risk for contagion is high,” the authors wrote in their study.

This curious ability of humans to pick up facial cues to identify sickness has actually not been studied much before. However, we’re all pretty well-versed with disease avoidance, the idea that the emotion of disgust is there to protect us from a disease. For example, a raw sewage pipe is likely to make your turn your face and walk the other direction because it could potentially contain harmful pathogens. As highlighted by this study, us humans might be even more skilled at avoiding diseases than we realize.

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