Why We Yawn

You probably yawn when you are tired or bored, and often just after you wake up. Your mouth opens wide, you take a long, deep breath, and then you breathe out again. The whole thing usually lasts only a few seconds, and once it starts, it can be very hard to stop. Most of the time, you do it without even thinking about it.

Everyone yawns, from adults to young children. Even babies do it: doctors have seen them yawning on scans, months before they are born. Many animals yawn too. If you have a cat or a dog, you have probably seen this, and lions, horses and monkeys do it as well.

In humans, yawning is also contagious: it can pass from one person to another. Imagine a quiet classroom on a warm afternoon. One student yawns, then another, and soon it goes around the room like a wave. Seeing someone yawn is not the only trigger. Even hearing a yawn, or just reading about one, can make you do it too.

Very young children are different, though. Babies yawn, but they do not seem to "catch" yawns from the people around them. This ability appears to develop later, during childhood.

So why do we yawn? The surprising answer is that scientists are still not sure. For a long time, many people believed that we yawn because our bodies need more oxygen. It is an easy idea to believe, since a yawn brings a lot of air into the body.

However, when scientists tested this idea, their experiments did not support it. For example, breathing air with extra oxygen did not seem to make people yawn less.

Today, scientists are studying other ideas. One is that yawning helps to cool the brain a little, in the same way that a fan stops a computer from getting too hot. Another is that it helps the body and brain to move between sleep and being awake. This could explain why we often yawn just before we go to bed and just after we wake up.

Perhaps there is more than one answer, and scientists will need more experiments to find out. Until then, yawning will stay a small mystery: something we all do without knowing exactly why. And if you have yawned while reading this text, don't worry. That is completely normal!