There are many fascinating mysteries about our shared human existence, and arguably one of the most intriguing is the act of yawning.

We yawn when we are tired or bored or even when we merely see others, including animals, doing it—but why? Discover what science has to say about the subject.

Causes and effects 

While experts don’t have all the answers for this phenomenon, they offer some theories, many of which are related to the brain. One posits that yawning’s main purpose is to simply perk up the mind when it’s understimulated or drowsy, primarily by causing the face and neck muscles to stretch, which then increases heart rate and blood flow. (This hypothesis would also explain why we sometimes do a full-body stretch during or after yawning.) Another belief is that yawning may serve as a self-defense mechanism of sorts for the brain by cooling it down when its core temperature rises.

Curiously contagious 

We’ve all experienced contagious yawning: the tendency to involuntarily mimic others, even a fourlegged friend, engaging in the act. This is thought to be a reflexive form of empathy, much like how we may mirror someone’s actions when they laugh or cry—especially if we personally know them.

Warning signs

Nobody would normally complain about having a good yawn; however, it may be a red flag if it happens in excess. In general, regularly yawning three times within fifteen minutes is considered extreme unless there’s an obvious cause, such as watching TV or listening to a boring lecture. If you notice that you’re yawning all the time, discuss the situation with your doctor since it could be a sign of a serious medical condition, such as stroke, heart attack, or sleep apnea