Question

Why do we yawn?

Answer 1

When we are bored or tired, we just don't breathe as deeply as we usually do. As this theory goes, our bodies take in less oxygen because our breathing has slowed. Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood.

Also when we start to yawn, powerful stretching of the jaw increases blood flow in the neck, face, and head. The deep intake of breath during a yawn forces downward flow of spinal fluid and blood from the brain. Cool air breathed into the mouth cools these fluids. Together these processes may act like a radiator, removing [too hot] blood from the brain while introducing cooler blood from the lungs and extremities, thereby cooling [brain] surfaces.