Psychologist Paul Ekman spent decades researching why the face gives us away even when the mouth is smiling politely. His answer is surprisingly simple: genuine emotions don't just show up around the lips — they appear in the eyes, the pupils, and in flickers that last only fractions of a second. These signals aren't courtroom evidence, but they are telling clues. One sign on its own means very little. Several appearing together? That's worth paying attention to.
1. The Duchenne smile is missing
French neurologist Guillaume Duchenne discovered that a genuine, joy-driven smile doesn't just move the mouth — it also engages the muscles around the eyes. This is known as the Duchenne smile. Research suggests that about 71% of people can produce it deliberately, and studies have found that a faked good mood can trigger this eye involvement just as often as real happiness. So it's not a perfect lie detector on its own.
Still, when someone smiles purely out of politeness — pulling up the corners of their mouth while the upper half of their face stays completely still — something feels off. The smile looks frozen, almost hollow. Most people can't quite put their finger on what's wrong, but the disconnect between the animated lower face and the expressionless eyes registers instinctively.
2. No crow's feet around the eyes
Closely linked to the Duchenne smile, but worth noting separately: genuine joy creates tiny wrinkles — crow's feet — at the outer corners of the eyes. These come from the contraction of the orbicularis oculi muscle, the ring of muscle surrounding the eye socket. If someone's mouth is smiling but the skin around their eyes stays perfectly smooth, that can raise a quiet alarm.
That said, this signal alone isn't definitive. Some people can consciously produce this effect too, so it's always best weighed alongside the other signs rather than in isolation.
3. An asymmetrical smile
Research suggests that forced or deliberate smiles tend to be more asymmetrical than spontaneous ones. When a smile is manufactured, the left side of the face typically moves more strongly — likely because the brain's right hemisphere plays the dominant role in emotional expression. The exact mechanism is still debated among researchers, and even genuine emotions don't always appear perfectly symmetrical.
Even so, a slight unevenness in the line of the mouth might seem like a minor detail — but it almost always registers subconsciously. Something feels rehearsed, slightly off. The other person may not be able to say why the gesture feels insincere, but their gut picks it up.
4. A momentary lip press and pupil changes
The hardest signals to conceal are the microexpressions Ekman documented so thoroughly — emotional flickers that cross the face in milliseconds, too fast to consciously suppress, yet still perceivable. One of the most telling: the lips briefly narrow during a smile, almost disappearing for a split second, as if the person involuntarily presses their mouth shut before returning to the smiling expression. This tiny movement often signals suppressed tension or irritation.
The face rarely lies perfectly — it just tells the truth too quickly for us to catch it.
Pupil changes can also be revealing, though perhaps not in the way most people expect. Pupils tend to dilate in response to strong emotion — whether that emotion is pleasant or unpleasant — because dilation primarily reflects arousal level, not whether an experience feels good or bad. This change is only a fraction of a millimeter and is practically impossible to measure with the naked eye. In everyday conversation, however, the overall cluster of subtle signals around the eyes often communicates far more than any polite words.
Don't jump to conclusions
It's important to keep context in mind. Someone might look tense or show these signs simply because they're tired, distracted, or dealing with something completely unrelated to you. These four signals only become genuinely meaningful when they appear together, repeatedly, across an interaction — not as isolated moments in a single conversation.
If you're curious about how emotions show up in everyday behavior and relationships, exploring the basics of body language can sharpen your instincts considerably.
