Sick and tired: identifying ill people at a glance

Empathy be damned. Among people who do not work in the health services there seems to be a compulsion to avoid sick folk.

This is not a recent behaviour, and may indeed be something innate. Certainly, as far back as the Fourteenth Century, the Italian author Giovanni Boccaccio noted widespread and urgent desires among the healthy to avoid the diseased.

In the introduction to his masterpiece, The Decameron, he observed that among the living “divers apprehensions and imaginations were engendered in the minds of such as were left alive, inclining almost all of them to the same harsh resolution, to wit, to shun and abhor all contact with the sick and all that belonged to them”.

Mind you, Boccaccio was writing about the Black Death, a plague that produced dreadful and highly visible symptoms – meaning that it was pretty easy for the living to identify the soon-to-be-dead.

Not all illness is as obvious, or as serious, as plague, of course – which raises the question of whether humans can identify others who are only mildly ill.

The answer, it seems, is yes, and in multiple ways – with new research suggesting that people can identify others with a mild bacterial infection as early as two hours after they contract the illness.

In 2014, a team of neuroscientists from the Karolinska Institute in Stockholm, Sweden, showed that sick people (in this case, a control group given a mild endotoxin called lipopolysaccharide) developed a distinctive and unpleasant body odour – a signal to the healthy to keep clear.

A year later, scientists from the same facility established that infected people tended to walk more slowly than their healthy counterparts – and that observers readily identified gait change as a sign of illness.

In a paper just published in the journal Proceedings of the Royal Society B, the Karolinska Institute once more takes the lead in the sickness detection stakes, with researchers led by John Axelsson reporting that untrained observers use facial cues to deduce the presence of illness in others.

To make their finding, the team recruited 32 volunteers and injected half of them with an Escherichia coli endotoxin – enough to induce mild symptoms – with the remainder receiving a placebo treatment. All volunteers then had their faces photographed two hours after the injection.

The photos were presented to 62 untrained observers, who were each asked to state whether he or she thought the person in the picture was healthy or sick. This netted a total of 2945 responses.

The results were significant. Axelsson and his colleagues found that over all 41% of photos were identified as showing a sick person. There were a substantial number of false hits, but a 70% correct result – well above chance.

The researchers write, “Acutely sick people were rated by naive observers as having paler lips and skin, a more swollen face, droopier corners of the mouth, more hanging eyelids, redder eyes, and less glossy and patchy skin, as well as appearing more tired.”

The scientists conclude that humans can detect acutely sick people “at a glance”. They encourage further research, to see if training can improve the ability, and to establish whether the facial cues remain constant across different diseases and ethnic groups.