Research has shown animals can smell sickness in others; but for humans, illness is all in the face, the Washington Post reports. A study published Wednesday in Proceedings of the Royal Society B reveals it's possible humans can tell if someone is healthy or sick—even if they aren't coughing or sneezing—just by looking at their face soon after infection. Researchers injected 16 people with lipopolysaccharide, a molecule found in bacterial membranes that activates the immune system and makes people feel sick, and later a placebo then took pictures of their faces two hours later. Researchers then had two groups of 60 or so people look at the photos for five seconds each, according to the Guardian. The first identified the individuals as either sick or healthy; the other ranked people's health based on facial properties.
Researchers, in what Science Magazine reports is the first study of its kind, found participants correctly identified sick people 52% of the time—or slightly better than guessing—and healthy people 70% of the time. They also found that pale skin and droopy eyelids were the biggest giveaways of a sick individual. A psychologist not involved in the study was surprised to find people are apparently better at judging health by looking at faces than determining other things, such as personalities. "We probably judge the health in other people all the time,” says study co-author John Axelsson. Experts say this could be an evolutionary trait to help humans avoid getting sick. (Another study found we are the most attracted to the faces around us.)