People may be able to detect whether someone is ill simply by looking at the individual's face—a finding that could help people stave off infections and could eventually help physicians improve their diagnoses, according to a new study in Proceedings of the Royal Society B.
For the study, researchers took pictures of 16 people before injecting them with lipopolysaccharide, a molecule found on many bacteria that prompts an immune system response and generates feelings of illness. About two hours after the injection, the researchers took another picture. They also photographed the participants on a separate day when they had given them a placebo injection.
The researchers then asked two groups, each including about 60 people, to examine the photos. The first group was asked whether the photographed individuals looked sick or healthy, while the second group was asked to rate how tired or alert the subject looked on a scale of one to seven. The second group also answered questions about subjects' facial cues, such as redness or paleness of skin.
The researchers found that the observers were able to detect an immune system response somewhat better than random chance: On a scale of 0.5 to 1, where 0.5 is entirely random, observers had an average score of 0.62. Overall, according to the study, observers accurately judged pictures of 13 participants and struggled with the images for three participants. According to STAT News, the observers incorrectly rated as ill about 30% of the pictures of healthy subjects.
The researchers also found identified several facial cues that observers correctly associated with sickness: drooping mouth, heavy eyelids, facial swelling, red eyes, and paleness. The researcher wrote, "Our findings suggest that facial cues associated with the skin, mouth and eyes can aid in the detection of acutely sick and potentially contagious people."
John Axelsson—a neuroscientist at the Karolinska Institute in Sweden and the lead author on the study—said the study's findings could improve public health by helping people and clinicians more quickly spot illness, which in turn could help people stave off infection. As he explained, if people wait until someone's coughing or sneezing, it might be too late. "We are trying to tap into these first cues," he said. Axelsson added that the findings could eventually help improve technology designed to track the spread of illness.
Separately, David Perrett—a psychologist and researcher at the University of St. Andrews in Scotland, who wasn't involved in the study—said that he was "surprised" by the results. Before this study, no one had determined whether humans could sense "experimentally induced sickness" by looking at someone's face, but he said the study demonstrated that "sickness judgments turn out to be far more reliable" than other visual judgments.
But Mark Schaller—a psychology professor at the University of British Columbia, who wasn't involved with the study—cautioned against putting too much weight in the findings, pointing out that the study showed people incorrectly labeled an individual in a photo as being sick 440 times out of 1,215 . "They are only semi-accurate," he said. "It's a useful reminder of the fact that when we humans use superficial characteristics as sickness cues … those superficial features often lead us astray, with the consequence that we may often respond to healthy people as though they are sick."
Axelsson acknowledged that the study was limited in both size and scope, noting that the study assessed only visual cues a few hours after the subjects started looking sick, as opposed to a longer timeframe. He also noted that the study participants were not racially diverse, generally involved young white adults, which means that the results were not generalizable (Blau, STAT News, 1/2; Guarino, "Speaking of Science," Washington Post, 1/2).
Understand the wellness spectrum
Programs aimed at promoting healthy habits among employees are likely to lead to improved employee engagement and productivity—but they're unlikely to reduce the total cost of care. To do that, you'll need to take a population health approach.