Individual differences in sick face sensitivity: females are more sensitive to lassitude facial expressions than males

Abstract

Lassitude—characterized by drooping eyelids, pale and slightly parted lips, and drooping corners of the mouth—is an emotional expression exhibited when people are sick. Here, we tested the hypothesis that there may be individual differences in the ability to recognize lassitude facial expressions. Adults from an undergraduate subject pool in the U.S. (N = 280) viewed images of healthy faces and the same people's faces when they were sick with a naturally occurring contagious illness, rating them on six dimensions theorized to index latent lassitude perception: safety, healthiness, approachability, alertness, social interest, and positivity. We found each dimension loaded positively onto latent lassitude perception, consistent with our hypothesis that these dimensions tap unique but related constructs. Participants' sex predicted their latent lassitude perception, with females showing higher accuracy than males. Our findings suggest there are sex differences in sick face perception, much like the perception of other nonverbal expressions. This is the first study, to our knowledge, to discover a female advantage in recognizing natural lassitude expressions. We discuss possible evolutionary mechanisms, such as the Primary Caretaker Hypothesis, and implications for public health.