🥱 Why do we yawn when someone else yawns?

Yawning is a familiar gesture. It often appears when one is tired or when changing states of alertness, for example at the moment of falling asleep or waking up. However, it has a unique aspect: it is contagious. Seeing someone yawn, or even reading the word, can be enough to trigger a yawn in another person.

Yawning corresponds to a deep inspiration accompanied by a wide opening of the mouth and a stretching of the facial muscles. This behavior is observed in many vertebrate species, notably mammals and some birds. Its exact function remains debated, but several physiological mechanisms have been studied experimentally.


Among the studied hypotheses is that of brain thermoregulation. According to this theory, yawning would promote blood circulation and the entry of cooler air into the nasal cavities, which could help slightly cool the brain. Several experimental works support this, notably according to a review published in Frontiers in Neuroscience on the thermoregulatory theory of yawning.

The contagion of yawning constitutes a distinct phenomenon. Experiments have shown that the probability of yawning increases when a person observes someone yawning or looks at images showing this behavior. Brain imaging studies suggest that this phenomenon involves regions of the brain related to imitation and social processing. A study using functional MRI thus showed the activation of brain networks involved in the perception and reproduction of observed actions according to a brain imaging study published in NeuroImage.

The contagion of yawning also seems influenced by social relationships. Several studies indicate that it occurs more often between close people, such as friends or family members, than between strangers. This observation suggests a link with mechanisms of social synchronization or empathy.

The phenomenon is not unique to the human species. Forms of contagious yawning have also been observed in several social species, notably in chimpanzees and some other primates. In these groups, contagion appears more frequent between individuals with close social bonds, which reinforces the idea that this behavior could play a role in social coordination.

Even though some aspects are still being studied, research shows that contagious yawning relies on real mechanisms involving the observation of a behavior, the processing of social interactions, and the activity of brain networks related to imitation. A daily gesture that seems trivial thus reveals processes of brain functioning and interactions between individuals.