A Duchenne smile is a smiling facial expression resulting from true happiness, characterized by engaging the muscles around a person's mouth and eyes. The expression is named after Guillaume-Benjamin-Amand Duchenne (de Boulogne), a French neurologist who greatly advanced the science of electro-physiology.
Duchenne studied the conductivity of neural pathways during his lifetime in France, which ranged from 1800 to 1875. He studied the electrical properties of tissues and cells, and he defined the fundamental expressive gestures of the human face, associating each with a specific facial muscle or muscle group. He discovered that a genuine smile, one that results from genuine happiness or pleasure, engaged the muscles around the mouth and eyes, unlike a fake smile.