Science has finally studied yawning — and what researchers found might actually change how you feel about doing it in public

I have spent a significant portion of my adult life apologising for yawning. In meetings, at the theatre, at dinner parties, at the dinner table, once memorably at my own birthday, I have produced an enormous, jaw-cracking, eye-watering yawn and immediately felt compelled to say something like “terribly sorry, it’s not the company” – which everyone knew was, at best, partially true.

It turns out I owe nobody an apology. I was cleaning my brain.

A new study from UNSW Sydney, published in Respiratory Physiology & Neurobiology, has used real-time MRI scans to observe what happens inside the head and neck when people yawn. The findings are, by the understated standards of academic research, rather extraordinary.

When you yawn – really yawn, not the fake yawn you deploy in meetings to see if it’s contagious – cerebrospinal fluid and venous blood move out of the skull together. This is the opposite of what happens during a deep breath, when cerebrospinal fluid moves into the skull. Yawning, in other words, appears to do something entirely different to the brain’s fluid dynamics than any other breathing-adjacent action, and the researchers believe it may be helping to flush waste products from the brain.

Now, cerebrospinal fluid is the clear liquid that surrounds your brain and spinal cord – think of it as the brain’s cleaning fluid, cushioning, protecting, carrying nutrients in and waste products out. And the accumulation of waste in and around the brain has been linked to neurodegenerative diseases including Alzheimer’s and Parkinson’s. The researchers are appropriately cautious – this is a small study of 22 participants and they are careful to describe it as speculative – but the implication is fascinating: your enormous, rude, public yawn may be doing something genuinely useful for long-term brain health.

“There has been speculation that yawning can help clear waste from the brain,” said Professor Lynne Bilston, from UNSW’s School of Biomedical Engineering, “but so far there has not been solid proof. Our research suggests that yawning can play a role in cleaning brain fluid, which would most likely happen close to bedtime.”

Close to bedtime! When no one is watching! Typical.

The method was magnificent

Here is my favourite detail in this entire story, and I assure you it is real: in order to get their 22 participants to produce genuine yawns while lying inside an MRI machine, the researchers showed them videos of other people yawning. And crocodiles. They showed them yawning crocodiles.

This is because yawning is contagious – you may well have just yawned reading the word – and the team needed authentic yawns rather than the pretend version.

The MRI scans were taken at the level of the C3 vertebra in the upper neck, where blood and cerebrospinal fluid pass as they travel to and from the brain. The real yawn produced a completely different fluid flow signature to the fake one. Only the genuine article – triggered, apparently, by a crocodile doing it first -produced the combined outflow of cerebrospinal fluid and venous blood that the researchers were looking for.

“Yawning remains very mysterious, even though it’s a primordial process that has been preserved throughout evolution. We know that crocodiles yawn, so we think dinosaurs also yawned,” said Adam Martinac, the paper’s corresponding author. “It’s unlikely that crocodiles and dinosaurs are yawning because of a social response, such as being bored by other crocodiles or dinosaurs. So there is likely something more fundamental going on.”

I find it deeply soothing that we share this reflex with the Cretaceous period. Whatever else may divide us from the dinosaurs – the thumbs, the Netflix subscriptions, the crippling awareness of our own mortality – we are united across 66 million years by the exact same urge to open our mouths as wide as they will go and let everything reset.

Also: your yawn is unique

In what may be the finding I least expected from a study about yawning, the researchers also discovered that each person appears to yawn in their own individual way – the complex movement of the tongue during a yawn is consistent within each person but different across people. It is, as Martinac puts it, “almost like a fingerprint.”

I have spent considerable time since reading this attempting to yawn in front of a mirror and describe the tongue motion. My wife has asked me to stop. Science rarely arrives without personal cost.

The thermoregulation angle

The researchers further suggest that yawning may be a way for the brain to regulate its own temperature. The brain runs about one degree Celsius hotter than the rest of the body, and venous blood leaving the brain is slightly warmer than arterial blood entering it. When you yawn, cooler arterial blood flows in to compensate for the outflow of the warmer venous blood and cerebrospinal fluid.

“A hot brain is not a good thing because there is a risk of cell damage, seizures and cerebral swelling,” said Martinac. The brain, it turns out, operates within a very narrow temperature band. And yawning may be one of the mechanisms by which it keeps itself within range.

Which means that next time you are somewhere warm and you feel that irresistible urge to open your mouth in a way that makes you look like a yawning hippopotamus, you are not being rude. You are performing active thermal management of your most important organ.

I suggest you explain this to whoever is watching.