Ask Dr Bec: What causes a yawn – and why are they contagious?

Narrabri-based scientist Dr Bec Thistlethwaite contributes a column to The Courier on the science in our daily lives. Readers are invited to send their science questions in to Dr Bec via [email protected]

What causes a yawn – and why are they contagious?

Yawning is one of those everyday things we rarely think about – until we’re suddenly doing it non-stop.

But what actually causes a yawn?

And why do we sometimes yawn just because someone else does?

Scientifically, a yawn is a reflex: a deep breath in, stretching the jaw and filling the lungs, followed by a slow exhale.

For a long time, people thought yawning was just about bringing more oxygen into the body, but that idea doesn’t hold up – research shows we yawn even when oxygen levels are normal.

A more recent theory? Yawning helps cool the brain.

Just like a computer, the brain works best at a certain temperature.

Yawning pulls in cool air and increases blood flow to the brain, which may help regulate its temperature and keep us alert – especially when we’re tired or bored.

So what about the contagious part?

That’s where things get really interesting.

Seeing someone yawn – or even reading about yawning – can trigger a yawn in others.

Scientists believe this is linked to social bonding and empathy.

In fact, studies show you’re more likely to ‘catch’ a yawn from someone you know well.

It’s thought to be the brain’s way of mirroring others, a behaviour that helps us connect and understand each other.

Some animals, like chimpanzees and dogs, also show contagious yawning, suggesting it plays a role in group communication and shared states – like saying, “Hey, it’s time to rest,” without using words.

Yawning isn’t just about being tired.

It’s a complex blend of biology, brain cooling, and social connection.

And now that you’ve read this? There’s a pretty good chance you’re yawning too.