New research published in Scientific Reports raises questions about the link between attraction and pupil dilation.

“There is an enormous body of literature which measures attraction to various aspects of facial appearance, from which we’ve built quite complex models of face preferences and signalling of health and personality via the face,” said Fhionna R. Moore of the University of Dundee, the corresponding author of the study.

“However, the majority of this work measures attraction by asking participants to rate their preference for a face compared to another, or how ‘attractive’ they find the face on a 1-7 scale,” she told PsyPost. “We know very little about whether these self-reported ratings correspond to sexual attraction, more general attraction, or something else entirely.”

The two-part study used an eye-tracking device to measure the changes in pupil diameter of 109 women as they viewed images of male faces. Previous research indicates that the pupils dilate in response to arousing imagery.

But the researchers failed to find significant relationships between women’s pupil diameter change and their ratings of facial attractiveness.

“That we still don’t know what we’re tapping when we measure attractive ratings,” Moore explained. “These don’t correlate in our studies with a measure of physiological arousal (pupil diameter change), so we can’t be sure that they tell us anything about a physiological response to a face (e.g. due to sexual attraction, or perceived threat).”

The researchers did find that pupil dilation was linked to viewing male faces with higher levels of testosterone. But it is unclear whether this physiological indication of arousal was provoked by sexual interest or perceived threat.

“This was a small scale study, which raised more questions than it answered,” Moore said. “We would like to conduct a further series of studies now to test relationships between perceptions of faces (how sexually attractive this face? How threatening is this face?), pupil diameter change, and other measures of physiological arousal.”

The study, “Women’s self-rated attraction to male faces does not correspond with physiological arousal“, was co-authored by S. Hagerman, Z. Woolard, K. Anderson, and B. W. Tatler.