Psychology of smiling: Psychology says the barista whose smile crinkles their eyes isn't just doing customer service; Ekman's research found a real "Duchenne" smile is physiologically tied to genuine enjoyment

You know the smile. The barista hands you your oat milk latte, and for a split second, the corners of their eyes crinkle up along with their mouth. It’s not the flat, polite smile you get from a stranger at a coffee shop. It turns out that gut feeling is based on real science. The classic 1990 study, ‘The Duchenne smile: emotional expression and brain physiology. II,’ by psychologist Paul Ekman and colleagues, found that smiles involving the eye muscles do generally reflect real positive feelings, at least for a group of people. The Duchenne smile has been of interest to psychologists for decades.

What exactly is a Duchenne smile
The normal smile involves one muscle, the zygomatic major, which pulls the corners of your lips up and back. Duchenne smiles also engage the orbicularis oculi, the muscle around your eye that produces those little crinkles at the corners. The name is derived from the 19th-century French physician, Guillaume Duchenne, who studied this muscle pattern through electrical stimulation of the face.

In the study, Ekman and his co-authors, Richard Davidson and Wallace Friesen, had people individually watch good movies meant to entertain them and bad movies showing distressing medical footage. While they watched, researchers recorded their facial movements, tracked their brain activity through EEG, and collected their own reports of how they felt. This research showed that the eye-crinkling Duchenne smile was more frequent during the pleasurable films than during the unpleasant ones. It was associated with a particular pattern in the brain linked to positive emotions, often described in terms of asymmetry between the two hemispheres of the brain. It also lined up with people’s own reports of feeling good. Regular smiles without eye involvement weren’t showing this pattern.

Why this isn't just a fun fact for your group chat
This could matter more in 2026 than you might realize. Millennials and Gen Z have always had to read performance from authenticity, whether that’s a coworker’s enthusiasm on a video call or a barista’s customer-service face. The Duchenne smile provides us with one small piece of evidence to help differentiate a smile that is “on” from one that is genuine.

But it’s worth being cautious here, because psychology rarely is as neat as a single headline suggests.

The catch: eye-crinkles aren't a lie detector
This is where it gets a little more nuanced, and frankly, a little more interesting. Subsequent research complicates the neat narrative. According to a 2009 study, ‘Can Duchenne smiles be feigned? New evidence on felt and false smiles,’ by psychologists Eva Krumhuber and Antony Manstead, people are actually pretty capable of producing the eye-crinkle on cue, even when they're not the least bit amused. In their experiments, a similar proportion of spontaneously and deliberately posed smiles displayed that eye-muscle activity, which means plenty of people can fake the crinkle if they try.

The key finding of the study is that “felt” and “false” smiles can be surprisingly similar in appearance: judges’ ratings suggested that the deliberate smiles were often just as Duchenne-like as the spontaneous ones. Therefore, the authors argue that the mere presence of eye constriction cannot be used as a reliable sign of genuine enjoyment, particularly when smile dynamics, like its duration and intensity, are considered.

Another layer was added by a 2021 paper in the journal Affective Science, which reanalyzed Duchenne smile research with a large data set of recorded smiles. This analysis suggests that eye constriction did indeed give some information about how positive a person really felt, but the magnitude and duration of a smile predicted actual positive feeling equally well and provided little additional information once accounted for. So the eye-crinkle is not an infallible tell. It's one piece of a much more complicated puzzle.

The paper also notes that when smile magnitude and duration were included in the analysis, eye constriction added little additional explanatory power to how positive people felt. That reanalysis shifts the emphasis away from the eyes as a unique tell and toward the broader timing and strength of the smile itself as the stronger signal.

So what should you actually take away from this
Don't go diagnosing every smile you see today. The honest, careful conclusion is this: on average, across groups of people studied in controlled environments, eye-crinkling smiles generally seem to be more strongly associated with reported pleasure and specific brain activity patterns than mouth-only smiles. That’s a real pattern, a measurable one. But that doesn’t mean every crinkly smile on a person’s face is a sign of them feeling pure joy in that moment, nor is it a foolproof way to catch someone lying. Actors, customer service professionals, or just people being polite can and do make that eye crinkle on purpose.

So next time your barista's eyes crinkle as they hand you your coffee, it's fair to feel a little warm glow of "oh, that felt real." Just take that thought loosely. Faces are adaptable, and emotions are complex, and even the scientists who devote their careers to studying this continue to discover new wrinkles in the story.

The broader perspective
The real interest in this research is not a party trick for identifying fake smiles. It reminds us that our faces are wired into our nervous systems and inner emotional lives in subtle, real, and only partly conscious ways, even if those ways are more accessible to us than Ekman's original theory suggested. The next time you catch yourself smiling to yourself, without meaning to, that's your body telling on you a little bit. In a world of curated selfies and performed positivity, there is something comforting about that.