First, let's start by busting one myth about yawning. A lot of people have the misconception that we yawn because our brains need more oxygen. However, several studies have shown that no matter how little oxygen is around a person, they won't yawn more. Even after exercise, when people in fact do need more oxygen, they do not yawn more frequently. Recent research says that the answer does lie in the brain, but that it is not a lack of oxygen , but rather it is because of the temperature of the brain. When we are exhausted the temperature deep in the brain increases. However, the brain operates best at a specific temperature, much like a computer. When you yawn, you bring in a lot of air from the outside into your mouth and ears. This air cools down the blood in your face and that helps cool down your brain. So yawning helps us to regulate our brain’s temperature.

This article is a summary of a video report from Vsauce.