Why do we yawn?
For grown-ups: the science
A yawn may help your brain cool down and shift between sleepy and awake.
The function of yawning is not fully settled. Leading evidence supports a role in brain thermoregulation and changes in arousal state, especially around sleep-wake transitions. Jaw stretching, facial muscle activity, and breathing during a yawn may contribute to cooling, though the precise mechanism remains under study. Contagious yawning is a separate social phenomenon in humans and some other animals, potentially involving social-attention or empathy-related brain circuits.
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Transcript
Your mouth opens wide during a big yawn. What is your body doing then?
When your body shifts from sleepy to more awake, a yawn may begin. Scientists think it may help your brain cool down and reset.
Stretching your jaw and breathing during a yawn may move warmth away from your brain. Scientists are still studying exactly how it works.
Seeing someone yawn can make your own yawn pop out. Brains may copy nearby people as part of being social, even though that is not what starts every yawn.
So, yawns may help your brain shift gears and cool down. Some parts are still a science mystery!