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Almost all animals yawn, from humans on down to lizards. It’s something we do every day, starting before we’re even born (babies yawn in utero). We do it when we’re tired — but we do it when we’re wide awake, too. Sometimes we do it just because we saw someone else do it. So what’s the deal with yawning?
When you yawn, you throw your head back, open your jaws wide, and inhale deeply through your mouth and nose. You briefly hold the breath and then slowly exhale it. Most yawns average 5 seconds in length and are accompanied by stretching. There’s something about that yawn-and-stretch combo that’s deeply satisfying. But does it serve any physiological purpose?
While a yawn looks simple enough on the surface, it’s actually surprisingly complex. There are many theories about why we yawn, and the newest and most promising one is that yawning is a means of cooling the brain. But more on that later.
Even thinking about yawning can make you do it. Ever tried to stifle a yawn? It’s one of those actions, like sneezing, that you have very little control over. For a long time it was believed we yawn as a way to get more oxygen and get rid of excess carbon dioxide. As far back as 400 B.C. Hippocrates suggested yawning was a means of expelling “bad air” from the body.
But recent research has mostly debunked this theory. In experiments, people were placed in environments with more or less oxygen, and it had no effect on how much they yawned.
We usually associate yawning with sleepiness or boredom, but research has found that we also yawn when we’re stressed. Researchers have observed athletes yawning more before they compete and paratroopers yawning before jumping out of a plane for the first time.
The fact that we yawn in a variety of situations — and not just when we’re tired or bored — has stumped researchers for years. One possible explanation is that yawning helps your brain and body shift from one state to another. It helps you wake up when you’re sleepy (and vice versa), it helps you feel more alert when you’re bored, and it helps you calm down when you’re anxious. But a new theory has emerged in the last few years that looks like it may finally be the answer.
Boredom, sleepiness, hunger, anxiety: What do these things have in common? Interestingly, they all seem to cause an increase in brain temperature.
The latest research suggests that we yawn to protect our brains from overheating. The brain is very sensitive to changes in temperature, and it functions best when it’s cool. When you yawn, it may be your body’s way of bringing cool air into your head to chill out your brain.
Usually, it just means you didn’t get enough sleep last night. But some health conditions can cause a person to yawn much more than usual. It’s rare, but some people yawn excessively when they’re having a heart attack.
Excessive yawning has also been observed in people with epilepsy, migraine headaches, schizophrenia, and multiple sclerosis. Interestingly, these conditions have also been linked with thermoregulatory dysfunction — when the body has trouble maintaining ideal temperature. People with epilepsy sometimes have bouts of yawning before a seizure, and yawning can also be a sign of an oncoming migraine. It could be that neurological disorders overheat the brain, and excessive yawning kicks in as a way to cool it down.
We’ve all experienced it — you see someone yawn, and suddenly you need to yawn. Even looking at a picture of someone yawning can trigger it. Yawns are undoubtedly contagious (and not just in humans), but there’s a lot of debate about why this is.
It could be that contagious yawning is a sign of empathy. One study conducted on children found that kids younger than four didn’t “catch” yawns. It’s around this same age that children develop the ability to empathize with others. The study also found that children with autism were less likely to yawn in response to another person’s yawn. In another study, college students took a personality test and were then shown video clips of yawning. The study found that less empathetic people were less likely to yawn contagiously.
Another theory of contagious yawning suggests it’s a primitive form of communication meant to keep a group vigilant and safe from danger. This actually works with the idea that yawning cools the brain. It could be that in groups, when one individual yawns, the rest pick up the behavior in order to maintain optimal brain function.
The brain-cooling theory seems to explain a lot about why we yawn, both spontaneously and contagiously. But for now that’s all it is — a theory. Future research may prove it true or debunk it entirely. There’s a lot we still don’t understand about yawning, but one thing’s clear. It’s a lot more than just a sign that you’re tired.