The Friday Question: Why Do We Yawn?

Over the past few weeks, I’ve received LOADS of really interesting questions to address in this Friday Question slot, many of which I had never wondered about, which is really cool! So, if you asked me something, keep your eyes open, over the next weeks and months I’ll be doing my best to find answers to all your questions. And if you think of a question, do email me at, others can attest that I am always very excited to receive mail, especially mail with questions. Today’s question was posed by the excellent Lara, whose blog posts always makes me feel like I want to be her friend, and also like I need to go take several million creative writing classes, so perfect is her way with words. Sorry this post was a long time coming, Lara…

I love questions with a simple answer I can easily understand, I love it when the world makes perfect sense. At the same time, there’s something about a question with no easy answer, something about the mystery of it, the sense that there is more out there to be discovered and understood. That is the joy of science, after all, both the wonder of knowledge and the knowledge that there is always more to learn. Why do we yawn is one of those questions without a single proper answer, instead we have a collection of possible theories that might explain what’s going on, or indeed that might not.

Wake me up, before you go

One of the major yawning theories, and the one that I have mostly been told in the past, is that yawning wakes your brain up. The theory goes that a big yawn increases blood flow to the brain, particularly to the area associated with co-ordinating movement, consciousness and memory. This helps the brain prepare for action, should action be necessary. From an evolutionary point of view, this would explain why we often yawn when we’re tired, or when we first wake up. These sleepy times moments are lovely when you’re snuggled up in bed, but if something big and bad was about to eat you, being sleepy and drowsy wouldn’t be the best way to survive. This theory suggests that yawning is like a warm-up drill for your brain, and it’s backed up by studies that show people often yawn before events that require them to be alert, like exams, or heading on stage. These studies aren’t conclusive, though, it’s impossible to assume that just because these people are about to do nerve-wracking stuff, it’s the nerve-wracking stuff that is making them yawn.

It’s getting hot in here

Another commonly heard theory, and this is another one that I’ve been told in the past, is that yawning cools your brain down.  You do a lot of thinking, day-to-day. Even when you’re not really thinking about anything very much at all, when you’re watching rubbish on TV and your brain is idly pondering whether you can be bothered to go make a cup of tea, your brain is still busy and complex and active. And, like any busy and complex and active machine, this might lead to some overheating. Of course, air doesn’t rush to your brain when you yawn, but the rush of cool air into your head may cool down the surrounding equipment. I actually quite like this theory, because it means every time I yawn I’m justified in believing that it’s because my brain has been working really hard at thinking, and needs a rest. This theory is supported by studies that show people yawn more commonly in winter months, which is presumably because the air is colder and will cool down the brain more effectively. Again, though, this is unlikely to be the whole story.

Get on up, when you’re down

Another theory thinks that yawning is linked to brain chemicals, and that the levels of chemicals hanging around have an effect on whether or not we yawn. For example, high levels of serotonin and dopamine seem to increase yawning. Unfortunately, no-one has any idea why this might be, unless it’s just that serotonin and dopamine get bored, and make you yawn for the fun of it. But that’s probably not it.

I feel your pain, man

The final yawning theory is linked to the fact that yawning is so contagious. For example, pretty sure that reading this article will have made most of you yawn, and quite possible everyone around you is now yawning. I’ve basically started a Friday yawning epidemic. The empathy theory of yawning is based on the fact that you’re more likely to yawn if someone you empathise with yawns, like a family member or close friend, or even just someone your own age or gender.   The idea is that yawning is based on your ability to share the feelings of another member of your group, something which also might have a distinct evolutionary advantage.

And, there you have it, no one conclusive answer to the question, I’m afraid, but lots of intriguing theories as to why we might yawn. The best part of it is that they’re probably all right, to a certain extent; yawning might be caused by different things at different times under different circumstances. This probably won’t stop me using the “my brain has overheated, look..” *yawn* excuse, though.


5 thoughts on “The Friday Question: Why Do We Yawn?

  1. Thank you Katie- both for the kind words and the excellent post. Yours always make me want to enroll in ALL the science classes; persuade you to be my friend for life and schedule blog posts with the military efficiency that you demonstrate 🙂
    I had only ever heard the first theory before but the second is definitely my favourite too – I wish I’d known of it when I was a teenager (“What, I’m over-heating, I’ve been thinking too much, I need a lie down. And some ice cream. STAT. Thanks Dad”)…. Xx

  2. Huh, I always thought/heard it was something to do with needing more oxygen and if you take deep breaths you won’t need to yawn… Obviously something I made up.

    • This is what my mother says about not hiccuping. Whenever I hiccup, she accuses me of not having been breathing properly otherwise, she says, my diaphragm wouldn’t have gone into spasm…oh guru Katie, is this true? 🙂

  3. Heya just wanted to give you a brief heads up and let you
    know a few of the pictures aren’t loading properly. I’m
    not sure why but I think its a linking issue. I’ve tried it in two different browsers and both show the same results.

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