Functional asymmetry in the human face: perception of health in the left and right sides of the face.

The expression of health on the human face, like beauty or emotions, is an important biological display. Previous findings of left-right functional asymmetry in facial attractiveness and the linkage of attractiveness and health in evolutionary biology notions have prompted the present study. A total of 38 pairs of left-left and right-right facial composites were viewed by 24 subjects on a computer screen, and the task was to decide which member of the pair looked healthier or there was no difference. The results revealed a significant interaction between face side and sex of face. Right-right composites of women's faces were judged significantly healthier than left-left, whereas in men's faces, no significant left-right difference emerged. As these results parallel previous findings of attractiveness in the identical set of faces, we propose that evolutionary biology notions linking the appearance of health and of attractiveness apply to the human face as well.