Topics The human body

Why do we yawn?

Nobody knows for certain why we yawn. A yawn is a long, deep breath with a wide-open mouth, and it shows up in people, other mammals, birds and even some reptiles, yet no single explanation has won out. The best-known ideas are that it helps cool the brain, that it shifts our state of alertness, and that it plays a social role. Each has some support and each has critics.

What makes it interesting is how ordinary and strange it is at once. We yawn when tired, but also when bored, and sometimes before something stressful. We even yawn when we see someone else do it, or read about it. Babies yawn before birth. The old idea that yawning tops up oxygen in the blood has not held up well in experiments.

An episode would lay out the main hypotheses, say what each one explains and where it falls short, and look at why yawns are contagious. It would be honest about the gaps. The hosts on bre are AI and can be wrong, so treat it as a curious tour, not a medical source.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. What a yawn physically isThe stretch of the jaw, the deep inhale, the slow exhale, and the muscles and brain regions involved.
  2. The oxygen idea and why it fadedThe old belief that yawns fix low oxygen or high carbon dioxide, and why experiments did not back it up.
  3. The brain cooling hypothesisThe proposal that a yawn helps regulate brain temperature, what supports it, and what is still debated.
  4. Yawning and alertnessWhy we yawn when drowsy, bored or waking up, and the idea that yawns shift the body between states.
  5. Why yawns are contagiousHow seeing, hearing or reading about a yawn can trigger one, and the open question of whether empathy is involved.
  6. Yawning across species and agesYawns in animals and in unborn babies, and what that suggests about how old the behavior is.
  7. What we still do not knowA plain list of unanswered questions and why such a common reflex is hard to study.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Tess. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Okay, I'll start with a confession. I've yawned twice since we started setting this up, and I'm not even tired.

  2. TessAI host

    Great, now I'm yawning too. Thanks. So is the answer just, you need more oxygen? That's what I was always told.

  3. breAI host

    That's the one most people were taught. It's also the one that didn't hold up well when researchers tested it.

  4. TessAI host

    Wait, so everyone's been wrong for decades? What's the replacement?

  5. breAI host

    There isn't a clean one. There are a few leading ideas: cooling the brain, shifting how alert you are, something social. I don't know which is right, and honestly, nobody does.

  6. TessAI host

    Okay, but real talk. A reflex that common, and we can't say what it's for?

  7. breAI host

    Pretty much. Which is why it's fun. Let's start with what your body is actually doing during one.

Questions people also ask

Does yawning mean you are tired?
Often, but not always. People yawn when drowsy, yet also when bored, waking up, or anxious. That pattern fits the idea that yawning is linked to changes in alertness, though scientists have not settled exactly what a yawn does or why it happens.
Is yawning caused by a lack of oxygen?
Probably not. This was a popular explanation for a long time, but experiments that changed oxygen and carbon dioxide levels in the air people breathed did not make them yawn more or less. Researchers now favor other explanations, though none is proven.
Why are yawns contagious?
It is not fully understood. Seeing, hearing or even reading about a yawn can set one off. Some researchers link it to social bonding or empathy, but that connection is debated, and not everyone catches yawns equally easily.
Do animals yawn too?
Yes. Yawning has been observed in many mammals, including dogs, cats and primates, and in birds and some reptiles and fish. Human babies also yawn before birth. That suggests it is an old behavior, though its purpose may differ between species.

Related topics

More: all 300 topics, the human body, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.