You meet someone for the first time, and within a second or two you’ve already decided something about them — whether you’d trust them, whether you’d want to keep talking. You didn’t run through a checklist. It just happened. And it turns out one of the things your brain quietly picks up on is something you’ve probably never once thought about on purpose: how much of the white of a person’s eyes you can see.
A study published in PLOS One by Mathias Boyer-Brosseau, Simon Rigoulot, and Sébastien Hétu looked at exactly that — the sclera, the white outer layer of the eyeball — and how the amount of it we can see shapes our first impressions. I came across this one on PsyPost, in a write-up by Eric W. Dolan, and it’s a great example of how a feature you’d never mention out loud can be doing real work behind the scenes.
Here’s what they did. They took photos of faces with neutral expressions from a well-known set called the Karolinska Directed Emotional Faces database. Then they digitally created two versions of each face — one showing a smaller amount of visible white (about 31.5% of the visible eye) and one showing more (about 43.8%) — while keeping everything else about the face identical. Then 162 adults rated the faces on four things: how much they’d trust the person, whether they’d interact with them, how attractive they found them, and where they’d place them in the social pecking order.
The result was remarkably consistent. Faces showing more of the white of the eye were rated as more trustworthy, more attractive, more sociable, and higher in social rank. And this wasn’t a quirk of one group — it held for male and female faces, and for male and female raters alike. A cue you never consciously register nudged four separate judgments in the same direction.
So why would the amount of white matter at all? Part of the answer is that these judgments are fast and effortless — a textbook case of automatic processing, the mental work that happens without conscious awareness or intent. You’re not deciding to evaluate someone’s sclera; your brain does it for you and hands you a feeling. The researchers offer two evolutionary psychology explanations — the idea that some mental traits stuck around because they helped our ancestors solve social problems. Humans are unusual in having such visible whites, which makes it easy to follow exactly where someone is looking, and reading gaze is a huge part of getting along with other people. On top of that, scleral exposure tends to peak in our early twenties and shrink as we age, so more white may quietly read as youth, health, and vitality.
There’s another layer here worth naming. A surface feature swaying a bunch of deeper judgments is basically peripheral route persuasion — attitude change that runs on superficial cues like attractiveness rather than on any real evidence about the person. And the ratings all moved together: faces judged attractive were also judged trustworthy, the classic attractiveness halo effect, where one good impression bleeds into all the others.
I have to admit, as a former college professor this one landed a little uncomfortably. I formed quick reads on students and colleagues all the time, and I’m sure I told myself those reads were based on something substantial. Studies like this are a good reminder that a chunk of my “gut” was probably running on cues about this superficial.
One honest caveat, and it’s a good one for anyone studying research methods: to add more visible white, the team had to make the eye itself a little bigger, so they couldn’t fully separate “more white” from “bigger eyes.” That’s a confounding variable — a second factor riding along with the one you care about, muddying the cause. The faces and raters were also mostly White, so we don’t yet know how far this travels across cultures.
What do you actually do with this? You can’t change your sclera, and please don’t try. The useful move runs the other direction: knowing your snap judgments can hinge on something this trivial should make you hold them more loosely. Next time you get an instant read on a stranger, treat it as a first guess, not a verdict — and give the person a second data point before you trust it.
If you’re taking a psychology course, scroll down — I’ve pulled out the key concepts this research illustrates, so you can see how a real study maps onto the terms you’re studying.
Psychology Terms in This Article
Automatic processing — Cognitive processing that happens without conscious awareness, intention, or effort, like recognizing a familiar face. In this study, participants weren’t deliberately measuring anyone’s sclera; the judgments of trust, attractiveness, sociability, and rank formed instantly and effortlessly, which is exactly why a cue this subtle could move them.
Evolutionary psychology — An approach that treats psychological traits as adaptations that evolved to solve recurring problems for our ancestors. The researchers use it to explain why we’d care about the white of the eye at all: highly visible sclera makes gaze-following easier (crucial for cooperation), and more white may signal youth and health — both things it would have paid off to notice.
Peripheral route persuasion — Attitude change driven by superficial cues, such as attractiveness or surface features, rather than by the quality of any real information. The whole effect here is peripheral-route in miniature: a small change to one facial feature shifted people’s overall impression of a stranger without adding a single fact about who that person actually is.
Confounding variable — An extra factor that varies along with the variable you’re studying, offering an alternative explanation for the result. Because increasing the visible white also slightly enlarged the eye, eye size is a confound here — the researchers can’t be fully certain whether it was the extra white or the bigger eye driving the friendlier ratings.
References
Boyer-Brosseau, M., Rigoulot, S., & Hétu, S. (2026). Scleral exposure influences social judgments of trustworthiness, attractiveness, sociability, and social rank in White faces. PLOS One. https://doi.org/10.1371/journal.pone.0348193
Dolan, E. W. (2026, July 28). People judge faces with more visible eye whites as more trustworthy and attractive. PsyPost.