What a Duchenne smile is
In 1862 the French neurologist Guillaume Duchenne de Boulogne stimulated facial muscles with a weak current and recorded what came out. He found that a smile is made by two different muscles: the zygomatic major pulls the corners of the mouth up, while the orbicularis oculi narrows the eye and gathers creases at its outer corner.
The first muscle obeys us freely — anyone can smile with the mouth at any moment. In most people the second one does not answer a deliberate command: it comes on by itself when the person genuinely feels good. Duchenne wrote that feigned joy is betrayed precisely by the stillness of the upper half of the face.
A century later Paul Ekman and Wallace Friesen named it the Duchenne smile and wrote its signs into the Facial Action Coding System: AU6 — cheek raise and eye narrowing; AU12 — lip corner pull. A polite smile is AU12 without AU6.
Three signs that give it away
- • The lower eyelid rises and the eye narrows from below — the eye looks slightly squeezed.
- • Creases gather at the outer corner of the eye — the so-called crow’s feet.
- • The cheek lifts, and the fold running from the nose to the corner of the mouth deepens and starts higher.
These are generated photorealistic portraits of fictional people. They illustrate visible smile features, not the actual feelings of a real person. Movement around the eyes alone does not prove sincerity.