Why Do We Yawn?

With the late nights, overly long lectures and recent exam cramming sessions, we often find ourselves yawning. But why do we do so? And what makes a yawn so contagious?

It was mainly believed that when we are tired or bored we do not breathe as deeply, so our body receives less oxygen. As carbon dioxide builds up in our lungs as a by-product, we need to expel it, and so we involuntarily yawn and breathe in a greater volume of oxygen. If carbon dioxide remained in the blood, it would poison us, so we yawn to expel the excess carbon dioxide. However, this has been disproved, as we yawn just as much in air rich in oxygen.

Another reason we are thought to yawn is to keep the brain from overheating. When you yawn and open your mouth wide, cool air moves in. The cool air narrows blood vessels in the brain and causes heat to be conducted faster. This action cools down the brain. When we eventually breathe out, the out flow of oxygen reduces the pressure of the brain.

Another theory is that we yawn due to the release of chemicals called neurotransmitters, such as dopamine and glycine, which control emotion, mood and other processes. Humans are not the only ones that yawn; the majority of animals do so also. It can be a defense mechanism for animals if their territory is attacked, as it apparently gives the impression that they are not threatened.

One thing we can guarantee though is that a yawn is contagious. We’ve all experienced it; when witnessing someone yawning, or even looking at a picture of someone yawning, you are stimulated to do the same. It is reported that 55% of people yawn shortly after seeing someone else yawn.  This is a positive feedback reaction and is believed to have been developed as a way of coordinating behavior and warning of changes in the environment.

Perhaps the most common place to see people yawning is a lecture theatre first thing in the morning. With the average yawn lasting six seconds long, just don’t let your lecturer catch you!

Jessica Hewitt-Dean


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