Why do we yawn?
No one knows for sure why we yawn. A leading theory is that yawning helps cool the brain. Yawns are also contagious, possibly linked to empathy.
Yawning is an involuntary reflex: we open the mouth wide, take a deep breath, stretch the jaw and then breathe out. People yawn when tired, bored or waking up, but also before stressful events. Athletes and parachutists often yawn just before they perform.
An old idea said we yawn to get more oxygen, but experiments in which people breathed extra oxygen or carbon dioxide did not change how often they yawned. Many researchers now favor the brain-cooling theory: the deep breath and stretch increase blood flow and bring cooler air in, which may help the brain stay alert.
Why yawns spread
Seeing, hearing or even reading about yawning can make you yawn. Contagious yawning is more common between friends and family than between strangers, and it does not usually appear until children are about four or five years old. Dogs and chimpanzees can catch yawns too.
Did You Know?
An average yawn lasts about six seconds. People even yawn before birth: ultrasound scans have shown unborn babies yawning in the womb.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.