Abstract
Humans evolved a behavioral immune system to avoid infectious disease, including the ability to detect sickness in faces. However, it is unclear whether the ability to recognize and avoid facial cues of disease is malleable, flexibly calibrated by experience. Thus, we experimentally tested whether we can improve adults' (N = 133) lassitude (sick) face perception, measuring their recognition, avoidance, and visual attention to naturally sick and healthy faces. Participants randomly assigned to a training about disease, but not a control group, were better at avoiding sick people. The disease-trained group also looked more equally between sick and healthy faces when identifying who was sick compared to the control group who looked longer at the sick faces than the healthy faces. Though we detected no group differences in time looking at the eyes and at the mouths, the disease-trained group used these features more to decide who was sick, reflecting key features of the lassitude expression. Our findings suggest that facial sickness perception may be flexible, influenced by experience, and underscore the need for future studies to test how to further strengthen this skill. Ultimately, developing interventions that use this sick face plasticity may reduce disease transmission.