smile

A smile is a facial expression in which the corners of the mouth turn upward, often producing a characteristic curve of the lips and, in many cases, widening the eyes. Smiles arise from a range of emotional states, including pleasure, amusement, relief, and social warmth, and can be voluntary or involuntary.

Physiology: The smile results from muscle activity around the mouth and eyes. The zygomaticus major pulls the corners of the mouth upward, while the orbicularis oculi can contract to cause eye squinting and crow's-feet around the eyes in genuine smiles. When only the mouth is involved, the smile may appear more controlled or polite.

Types and interpretation: Genuine smiles, often called Duchenne smiles, engage both mouth and eye muscles and reflect true positive affect. Non-Duchenne or social smiles may involve the mouth but not the eyes and are frequently used to signal friendliness, politeness, or social bonding without strong emotion. Smiles can also be used strategically to manage impressions.

Development and function: Humans smile from infancy; early smiles can occur without emotion, while social smiles emerge in the first months and increasingly coordinate interaction. Smiles facilitate trust, reduce perceived threat, and help regulate social interactions. Across many cultures, smiles signal friendliness, and people can recognize genuine smiles even when display rules differ.

Cultural and contextual variation: Display rules influence how openly and when to smile, and teeth showing is interpreted differently across cultures. Smiling is studied in psychology as a nonverbal cue contributing to emotion, social communication, and interpersonal influence.