Identification of acutely sick people and facial cues of sickness

Proc Biol Sci. 2018 Jan 10;285(1870):20172430. doi: 10.1098/rspb.2017.2430.


Detection and avoidance of sick individuals have been proposed as essential components in a behavioural defence against disease, limiting the risk of contamination. However, almost no knowledge exists on whether humans can detect sick individuals, and if so by what cues. Here, we demonstrate that untrained people can identify sick individuals above chance level by looking at facial photos taken 2 h after injection with a bacterial stimulus inducing an immune response (2.0 ng kg-1 lipopolysaccharide) or placebo, the global sensitivity index being d' = 0.405. Signal detection analysis (receiver operating characteristic curve area) showed an area of 0.62 (95% confidence intervals 0.60-0.63). 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. 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.

Trial registration: NCT02529592.

Keywords: disease avoidance; facial cues; health; social perception.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Disease*
  • Adult
  • Confidence Intervals
  • Cues
  • Double-Blind Method
  • Eye
  • Face
  • Facial Expression*
  • Female
  • Humans
  • Illness Behavior / drug effects
  • Illness Behavior / physiology*
  • Lipopolysaccharides
  • Photography
  • Signal Detection, Psychological
  • Volunteers
  • Young Adult


  • Lipopolysaccharides

Associated data

  • figshare/10.6084/m9.figshare.c.3951916