Why Do We Yawn? The Brain-Cooling Theory Explained

Every person on Earth yawns, every day. Many animals do it too. Yet scientists still do not fully agree on why. One of the most interesting answers is that a yawn helps cool your brain.

It is probably not about oxygen

A popular idea says we yawn to take in more oxygen. But when researchers changed the levels of oxygen and carbon dioxide that people breathed, yawning did not change in the way that idea predicts. So most scientists no longer think oxygen is the main reason.

The brain-cooling theory

Psychologist and biologist Andrew Gallup and his colleagues have studied yawning for years. Their idea is that a yawn works a bit like a radiator. The big stretch of the jaw and the deep breath of cooler air help bring cooler blood toward the brain and move warmer blood away.

Several findings fit this idea:

• In rats, brain temperature rose before a yawn and dropped after it.
• People held cold packs to their foreheads, or breathed only through their nose, and yawned less when watching videos of others yawning.
• People tend to yawn less when the air is hotter than the body, because breathing in warm air would not cool anything.

This could also explain why we often yawn when we are tired. Lack of sleep is linked to a warmer brain, and yawning is very common around bedtime and right after waking up.

Why yawns are contagious

You are more likely to yawn if you see, hear, or even read about someone else yawning. (Did you yawn just now?) Some research links contagious yawning to empathy and social bonds. Gallup has suggested it might once have helped groups stay alert together. Scientists are still testing these ideas.

The honest answer

Brain cooling is one of the best-supported theories, but there is no final answer yet. Other researchers think yawning mainly helps the brain switch between states, like sleeping and waking. It may well do more than one job.

Sources

• Science News: Latest research awakens debate over why we yawn
• The Naked Scientists: Why do we yawn? (interview with Gordon Gallup)

This article is for curiosity and learning only and is not medical advice. Very frequent yawning that is new or unusual for you is worth mentioning to a doctor.