Scientists aren’t completely sure, but a leading theory is that yawning helps cool the brain by drawing in a deep breath of air and increasing blood flow. Yawning also seems to help us shift between states, such as from sleepy to alert. The old idea that we yawn because we need more oxygen has not held up in experiments.

Why Do We Yawn? And Why Yawning Is Contagious

General information only. This article explains the basics and is not medical advice. For anything about your own health, talk to a doctor or other qualified professional.

You’ve probably yawned just reading this. A yawn lasts about six seconds, and humans start yawning before birth: ultrasound scans show babies yawning in the womb.

The main theories

Theory	Idea	Evidence
Brain cooling	A deep yawn brings in cooler air and boosts blood flow to the head	People tend to yawn less when the air is very hot or very cold
State change	Yawns help us wake up, or wind down, when switching activities	Athletes and performers often yawn before competing
Oxygen	We yawn because we need more oxygen	Experiments with extra oxygen didn’t reduce yawning

Why are yawns contagious?

Seeing, hearing or even thinking about someone yawning can make you yawn. Contagious yawning seems linked to social connection and empathy: people tend to “catch” yawns more from family and friends than from strangers. It usually develops at around four or five years old.

When we yawn most

Before sleep and right after waking
When bored, as the brain’s arousal drops
During transitions, like before a big event

Is yawning a lot a problem?

Usually not. Frequent yawning most often means you’re tired or not getting enough sleep. Here are tips on how to sleep better and reasons you might feel tired all the time. If excessive yawning comes with other unexplained symptoms, mention it to a doctor.

Why do we yawn?