Beauty might seem to be only skin deep, but Gettysburg College Psychology Professor Richard Russell has found that there is more depth to facial differences between men and women than presumed.

In a study published in Perception, Russell demonstrated the existence of a facial contrast difference between the two genders. By measuring photographs of men and women, he found that female faces have greater contrast between eyes, lips, and surrounding skin than do male faces. This difference in facial contrast was also found to influence our perception of the gender of a face.

Regardless of race, female skin is known to be lighter than male skin. But Russell found that female eyes and lips are not lighter than those of males, which creates higher contrast of eyes and lips on women's faces. By experimenting with an androgynous face, Russell learned that faces can be manipulated to appear female by increasing facial contrast or to appear male by decreasing facial contrast.

"Though people are not consciously aware of the sex difference in contrast, they unconsciously use contrast as a cue to tell what sex a face is," Russell said. "We also use the amount of contrast in a face to judge how masculine or feminine the face is, which is related to how attractive we think it is."

Given this sex difference in contrast, Russell found a connection between the application of cosmetics and how it consistently increases facial contrast. Female faces wearing cosmetics have greater facial contrast than the same faces not wearing cosmetics. Russell noted that female facial beauty has been closely linked to sex differences, with femininity considered attractive. His results suggest that cosmetics may function in part by exaggerating a sexually dimorphic attribute to make the face appear more feminine and attractive.

"Cosmetics are typically used in precisely the correct way to exaggerate this difference, " Russell said. "Making the eyes and lips darker without changing the surrounding skin increases the facial contrast. Femininity and attractiveness are highly correlated, so making a face more feminine also makes it more attractive."

In the photo, "Illusion of Sex," two faces are perceived as male and female. However, both faces are actually versions of the same androgynous face. One face was created by increasing the contrast of the androgynous face, while the other face was created by decreasing the contrast. The face with more contrast is perceived as female, while the face with less contrast is perceived as male. This demonstrates that contrast is an important cue for perceiving the sex of a face, with greater contrast appearing feminine, and lesser contrast appearing masculine.

Russell earned a bachelor's degree from Pomona College majoring in neuroscience and worked as a research assistant doing functional neuroimaging at Cambridge University. He received a Ph.D. in cognitive science from the Massachusetts Institute of Technology and completed postdoctoral research at Harvard University. His research interests are in visual cognition, aesthetics, and the perception of faces.