Yawn

Why Do We Yawn?

If you've ever felt sleepy late at night or bored during a movie, then you know what it's like to yawn! In fact, people aren't the only ones who yawn: watch a cat or dog get ready for a nap, and you'll probably see its mouth open wide and its tongue pop out as it takes a gigantic yawn. Well, whether you're talking about the yawn of a human being or the yawn of an animal, the reason for yawning is the same - to bring more oxygen into the blood and take more carbon dioxide out of the blood.

When you breathe in normally, you take oxygen from the air into your lungs. The lungs let the oxygen pass into your blood, which carries the oxygen all over your body. Every cell in your body needs oxygen, every minute of the day. When cells use up oxygen, they need to get rid of a waste product called carbon dioxide. The blood carries the carbon dioxide to the lungs, and the lungs exhale the waste out into the air. When you breathe out, you are getting rid of carbon dioxide.

When you are tired, bored, or sitting in a stuffy room, you breathe more slowly. When your breathing slows down, the lungs aren't able to bring in all the oxygen your body needs or get rid of carbon dioxide the way they should. When carbon dioxide can't get out of your body as fast as it normally does, it starts to build up in the blood. So in steps your brain to the rescue - it sends a message to your lungs to take an extra-deep breath called a yawn! A yawn makes you breathe in oxygen very deeply, and then breathe out carbon dioxide fully.

You can try a quick experiment to feel how much more deeply you breathe when yawning by putting your hand over your ribcage. Breathe in and out normally and you'll feel your chest move up and down, but only very slightly. Now pretend to take a big yawn, and feel what happens. As you breathe in, you'll feel your lungs inflate as they take in a lot of oxygen. When you breathe out, you'll feel them deflate as they get rid of lots of carbon dioxide. And speaking of practicing yawning, watch what happens if you ever yawn when someone else is around - chances are good that person will yawn, too! No one really knows why yawning is contagious, but it definitely seems to be.