Surprising influence of pupil size on attractiveness unveiled in new research

Can the size of your pupils affect how attractive you are? According to a new study published in Cognition, it just might.

Physical attractiveness has profound effects on social experiences and outcomes, often leading to positive perceptions and advantages, a phenomenon known as the “halo effect.” Attractive individuals tend to have more friends, higher earnings, and greater success in elections. Research on this topic has focused on facial features like prominent cheekbones, small noses, and especially the eyes. Large eyes are linked to youthfulness (a phenomenon known as neoteny) and attractiveness, enhancing the perceived “cuteness” of children and the appeal of adults.

Prior research has yielded inconsistent results about the effects of pupil size, with some studies suggesting that larger pupils enhance attractiveness, while others argue that smaller pupils, which reveal more of the iris and increase eye color and brightness, are more appealing. In this work, researchers Martina Cossu and colleagues strived to provide more conclusive results.

Experiment 1 included 252 participants recruited from Prolific. The researchers selected photos of four individuals (two males and two females), each in two different poses, and digitally manipulated them to have either constricted (20% of iris diameter) or dilated pupils (50% of iris diameter), resulting in sixteen photos. Participants were presented with pairs of these photos in a 2-alternative forced-choice task and asked to choose which version they found more attractive. The results revealed a preference for photos with constricted pupils.

Experiment 2 involved 257 participants who were shown 40 pairs of eyeshots, which included images of 20 males and 20 females with either blue or brown irises. Each eyeshot was digitally manipulated to have either constricted (20-25% of iris diameter) or dilated pupils (50-55% of iris diameter). Participants were asked to rate the attractiveness of these eyeshots on a slider scale ranging from 0 (very unattractive) to 100 (very attractive).

Free daily newsletter

The results consistently showed that faces with constricted pupils were rated as more attractive than those with dilated pupils, regardless of the iris color or the gender of the person in the photo.

Experiment 3 included 1199 participants from Prolific, divided into two independent samples. Participants were randomly assigned to one of three pupil size conditions: constricted (25% of iris diameter), neutral (40%), and dilated (55%), and asked to rate the attractiveness of a female eyeshot using the 100-point slider scale.

The results revealed that constricted pupils were rated as the most attractive, followed by neutral, and then dilated pupils. This linear effect of pupil size on attractiveness was consistent across both independent samples, reinforcing the finding that smaller, constricted pupils are perceived as more attractive.

Experiment 4 involved 799 participants from Prolific, who were asked to rate the attractiveness of headshots with manipulated pupil sizes (constricted or dilated) presented in both color and black-and-white versions. Each participant rated one version of the headshot using the same slider scale.

The results showed that constricted pupils were rated as more attractive than dilated pupils in both color and black-and-white images, suggesting that the increased attractiveness of constricted pupils was due to the brightness of the eyes rather than the color, as the effect persisted even when color was removed.

Experiment 5 was conducted in-lab with 307 participants who rated the attractiveness and brightness of 20 opposite-sex eyeshots. Each eyeshot was manipulated to have either constricted or dilated pupils. Attractiveness was rated on a 101-point sliding scale, while brightness was rated on a 7-point scale.

The results showed that eyes with constricted pupils were rated as more attractive and appeared brighter than those with dilated pupils. A mediation analysis confirmed that the increased perceived brightness of constricted pupils contributed to their higher attractiveness ratings.

Experiment 6 involved 300 participants recruited from Prolific, who were shown eyeshots with manipulated pupil sizes (constricted or dilated) while controlling for the colorfulness of the eyes. Participants rated the attractiveness and brightness of each eyeshot on a 100-point slider scale and 7-point scale, respectively. They likewise indicated how colorful the eyes appeared to be on a 7-point scale.

The findings revealed that even when the colorfulness of the eyes was controlled, constricted pupils were still rated as more attractive than dilated pupils, reinforcing the idea that the increased brightness associated with constricted pupils enhances perceived attractiveness, independent of eye color.

These studies confirm that regardless of eye color, pupil size significantly influences perceived attractiveness, with the brightness of constricted pupils playing a crucial role in enhancing their appeal.

A limitation noted by the authors is the reliance on manipulated images, which might not fully capture natural variations in pupil size.

The research, “Beauty is in the iris: Constricted pupils (enlarged irises) enhance attractiveness”, was authored by Martina Cossu, Maria Giulia Trupia, and Zachary Estes​.