An eye smile is a facial expression where the eyes visibly crinkle, narrow, and curve upward when a person smiles, making it look like the eyes themselves are smiling. It happens when the ring-shaped muscle surrounding each eye socket contracts at the same time the mouth pulls upward. This combination is what scientists call a Duchenne smile, and it’s widely considered the hallmark of a genuine, felt expression of happiness.
The Muscles Behind an Eye Smile
Two muscles work together to produce this expression. The first runs through the cheek and pulls the corners of the mouth upward. The second is a circular muscle that wraps entirely around the eye socket. When this eye muscle contracts, it draws skin inward from the temples and cheeks, narrowing the eye opening and producing the small radiating wrinkles known as crow’s feet. In genuine smiles, this contraction also causes a slight drooping of the upper eyelid, giving the eyes a warm, relaxed look.
When only the mouth muscle activates, you get what’s sometimes called a “social smile” or a “Pan Am smile” (named after the famously plastered-on grins of flight attendants). The mouth stretches wide, teeth may show, but the eyes stay flat and unchanged. The French neuroanatomist Guillaume Duchenne de Boulogne identified this distinction back in 1862, writing that the mouth can be willed into a smile, but only the “sweet emotions of the soul” force the eye muscle to contract. “Its inertia, in smiling,” he wrote, “unmasks a false friend.”
Why Most People Can’t Fake It
Only about 20% of people can voluntarily control the muscle around the eye that creates crow’s feet. For everyone else, that contraction happens automatically in response to genuine positive emotion, not on command. This is why eye smiles are so widely associated with authenticity. When someone’s eyes crinkle during a smile, observers instinctively read it as real.
That said, recent research complicates the picture. A study of 136 participants found that the eye crinkling may be less about genuine emotion and more about smile intensity. When researchers controlled for how strongly the mouth was pulling upward, the link between eye crinkling and actual felt amusement dropped significantly. In other words, a really big smile naturally recruits the eye muscles whether or not the person is feeling deep joy. The eye involvement might be more a byproduct of effort than a foolproof lie detector.
How People Judge Eye Smiles
Even if the science is more nuanced than “eye crinkle equals real happiness,” the social effects are clear. Research on how people judge faces found that trustworthiness ratings depend heavily on the eye region of a smiling face. A smiling mouth paired with flat or incongruent eyes, particularly angry-looking eyes, triggered strong feelings of untrustworthiness. Happiness judgments, by contrast, relied more on the mouth itself. So while the mouth tells people you’re happy, the eyes tell them whether to believe it.
This tracks with evolutionary thinking about the expression. Some researchers argue the Duchenne smile evolved as an honest signal of psychological well-being, essentially a way for people in good mental states to recognize and cooperate with each other. Because the eye muscle is difficult to fake, the signal stayed reliable enough to be useful over thousands of generations.
Eye Smiles in Pop Culture
The term “eye smile” is especially popular in K-pop fandoms, where idols known for particularly visible eye crinkles (like BTS’s Jimin or EXO’s Baekhyun) are celebrated for the trait. In this context, an eye smile refers to the way certain people’s eyes curve into distinctive crescent shapes when they smile, sometimes making the eyes nearly disappear. The feature is considered highly attractive and endearing, and fans often highlight it in photos and compilations.
In the modeling world, the concept goes by a different name. In 2009, Tyra Banks coined the term “smize” on Season 13 of America’s Next Top Model, blending “smile” with “eyes.” She taught contestants to smile with their eyes while keeping their mouths neutral or only slightly engaged, a technique for conveying warmth and intensity in photographs without a full grin. The skill became a staple of modeling advice, and “smize” entered mainstream slang.
What Happens When the Eye Muscle Is Blocked
Cosmetic injections for crow’s feet provide an unintentional experiment in what happens when the eye muscle can’t do its job. A study photographed patients before and after treatment that paralyzed the outer portion of the eye muscle, eliminating visible crow’s feet. Observers rated the pre-treatment smiles (with active eye muscles) as more genuinely felt, more spontaneous, more intense, and happier. Post-treatment smiles looked younger but were perceived as less authentic. The patients hadn’t changed how they felt, only whether their eye muscles could show it.
This finding highlights a real trade-off. Smoothing out crow’s feet can make a person look younger, but it also removes one of the most powerful social signals of genuine warmth. The resulting smiles read as flatter and less emotionally convincing to others, even when the person smiling is perfectly happy.
How to Spot an Eye Smile
Look for three things. First, crow’s feet: small lines fanning outward from the outer corners of the eyes. Second, raised lower eyelids: the skin beneath the eyes pushes upward, narrowing the eye opening from below. Third, a slight relaxation of the upper eyelid, which gives the eyes a softer, less wide-open look. Together, these changes make the eyes appear to squint slightly and curve into a crescent or half-moon shape.
A smile that only moves the mouth will leave the eye area completely unchanged. The upper face stays smooth, the eyes stay wide, and the overall effect feels stiff or posed, even if the person is showing a lot of teeth. The difference is easiest to spot in photos when you cover the mouth with your hand and look only at the eyes. In a genuine eye smile, the eyes alone still look happy.