yawning

Yawning is a reflex or voluntary action characterized by a wide opening of the mouth, a deep inhalation, and a prolonged exhalation, often followed by stretching. It is observed in humans and many non-human animals, including mammals and birds, and occurs across ages.

The exact neural mechanisms are not fully understood, but yawning involves brainstem circuits and the autonomic nervous system. It commonly occurs with fatigue, boredom, sleepiness, or as a transitional state between wakefulness and sleep. Observing others yawning can trigger contagious yawning.

Several explanations exist. The thermoregulation theory proposes yawning cools the brain by increasing blood flow and evaporative cooling. The arousal or social-communication theory suggests yawning helps maintain alertness and may aid social bonding or empathy. No consensus; yawning may serve multiple purposes or be a byproduct of other processes.

Contagious yawning has been documented in humans and some animals; it tends to be stronger among people who are more empathetic or familiar with the yawner. The phenomenon is linked to social context and may involve mirror-neuron–like mechanisms, but evidence is mixed.

Yawning is generally benign and normal. Excessive yawning can occur with sleep deprivation, fatigue, or certain medications. In rare cases, frequent yawning may accompany clinical conditions and warrant medical evaluation.