Yawning is something we all do, often without even thinking about it.
You might yawn when you’re tired, sitting through a long meeting, watching television late at night or even just because someone else yawned. In fact, there’s a good chance that simply reading about yawning has made you feel like doing one yourself.
But why do we yawn in the first place?
For something so common, scientists still don’t have a single, definite answer. Several theories exist, and while some ideas have been ruled out over the years, researchers continue to study exactly why our bodies produce this familiar reflex.
The short answer
Yawning is a natural reflex that involves opening your mouth wide, taking a deep breath and then slowly breathing out.
Although scientists don’t know its exact purpose, the strongest evidence suggests that yawning may help regulate brain temperature, increase alertness and signal changes in our level of wakefulness. It also appears to play an important role in social behaviour, which may explain why yawns are so contagious.
What happens when you yawn?
A yawn is much more than simply opening your mouth.
When you yawn, several things happen at once:
- Your mouth opens wide.
- You take a deep breath in.
- Your facial muscles stretch.
- Your jaw muscles contract.
- Your eyes may briefly close or water.
- You slowly breathe out.
The entire process usually lasts just a few seconds, but it involves a surprisingly coordinated series of muscle movements.
Why do we yawn when we’re tired?
This is probably the situation most people associate with yawning.
When you’re tired, bored or becoming sleepy, your brain is changing from one state of alertness to another. Yawning seems to occur during these transitions.
Scientists believe it may help increase alertness for a short time by stimulating parts of the nervous system and increasing blood flow to the brain.
That’s why you often notice people yawning:
- Just before going to bed.
- Shortly after waking up.
- During long lectures or meetings.
- While driving for long periods.
- During repetitive tasks.
It’s not necessarily the tiredness itself causing the yawn, but the change in your body’s level of alertness.
Does yawning cool your brain?
One of the leading scientific theories is known as the brain cooling hypothesis.
The idea is that yawning helps regulate the brain’s temperature.
When you take a deep breath and stretch your jaw muscles, blood flow around the head and neck increases. Cooler air entering the mouth and nose may also help slightly reduce brain temperature.
A cooler brain is thought to function more efficiently, potentially making you feel a little more alert.
While researchers continue to study this theory, several experiments have found evidence that supports the idea that yawning may help regulate brain temperature in certain situations.
Is yawning caused by a lack of oxygen?
For many years, people believed yawning happened because the body wasn’t getting enough oxygen.
It sounds logical.
You’re tired.
You take a deep breath.
You feel more awake.
However, research hasn’t supported this explanation.
Studies have shown that breathing air with higher oxygen levels doesn’t reduce yawning, and breathing air with extra carbon dioxide doesn’t make people yawn more often.
Today, scientists generally agree that oxygen levels are unlikely to be the main reason we yawn.
Why are yawns contagious?
Perhaps the strangest thing about yawning is how easily it spreads.
Someone yawns.
A few seconds later, you do too.
Sometimes even seeing a photograph of someone yawning—or simply reading about it—is enough to trigger one.
Researchers think contagious yawning may be linked to empathy and social bonding.
Brain imaging studies suggest that areas involved in understanding other people’s actions and emotions become active when we see someone yawn.
Interestingly, contagious yawning appears to be stronger between family members and close friends than between strangers.
Not everyone experiences contagious yawning to the same degree, and young children typically don’t develop it until they’re a few years old.
Why do animals yawn?
Humans aren’t the only creatures that yawn.
Many mammals do it, including:
- Dogs
- Cats
- Horses
- Chimpanzees
- Lions
- Elephants
Some birds and reptiles have also been observed yawning.
Although the reasons may vary between species, yawning often appears during changes in activity levels, such as waking up, resting or preparing to sleep.
In social animals, yawning may also play a role in communication within the group.
Can yawning mean you’re bored?
Yes—but probably not for the reason you think.
When you’re bored, your brain receives less stimulation.
Yawning may help increase alertness for a short period, making it easier to stay awake or refocus your attention.
So while boredom and yawning often occur together, boredom itself isn’t necessarily causing the yawn. Instead, both may be linked to reduced alertness.
Can you yawn too much?
Occasional yawning is completely normal.
However, excessive yawning can sometimes be associated with certain medical conditions or medications.
Frequent yawning has been linked with:
- Sleep disorders
- Severe sleep deprivation
- Some neurological conditions
- Certain medications, including some antidepressants
- Rarely, problems affecting the heart or nervous system
Most people who yawn frequently simply need more sleep or are particularly tired.
However, if you suddenly begin yawning far more than usual without an obvious reason—especially if it’s accompanied by other symptoms such as chest pain, fainting, weakness or difficulty speaking—you should seek medical advice promptly.
Common myths about yawning
“Yawning means you’re rude.”
Not at all.
Although yawning during a conversation may seem impolite, it’s usually an automatic reflex rather than a sign that someone isn’t interested.
“Only tired people yawn.”
False.
People also yawn when they’re waking up, relaxing, bored, stressed or even anticipating an activity.
“Yawning means your body needs more oxygen.”
This was once widely believed, but scientific research has largely disproved this theory.
“You can catch a yawn.”
In a way, yes!
You can’t catch yawning like an illness, but seeing, hearing or even thinking about yawning can trigger your own yawn.
Fun facts about yawning
- Even unborn babies have been observed yawning during pregnancy scans.
- Simply reading about yawning makes many people yawn.
- Dogs can “catch” yawns from humans.
- Most yawns last between four and seven seconds.
- Scientists are still debating exactly why we yawn, despite studying it for decades.
Final thoughts
Yawning is something we all experience, yet it’s still one of the body’s most fascinating mysteries.
Researchers have made huge progress in understanding what happens during a yawn, but there’s still no single explanation that answers every question.
The strongest evidence suggests yawning helps regulate alertness, may cool the brain and plays an important role in social behaviour through contagious yawning.
So, the next time someone accuses you of being bored because you yawned, you can tell them it’s probably a little more complicated than that.
Frequently Asked Questions
Why do people yawn when someone else yawns?
Scientists believe contagious yawning is linked to social behaviour and empathy. Seeing another person yawn can automatically trigger the same response in your own brain.
Why do I yawn even when I’m not tired?
Yawning doesn’t only happen because of tiredness. It can also occur when you’re bored, waking up, stressed or moving between different levels of alertness.
Can yawning be a sign of illness?
Occasional yawning is perfectly normal. However, sudden or excessive yawning without an obvious cause, particularly alongside other symptoms, should be discussed with a healthcare professional.
Is it true that reading about yawning makes you yawn?
Yes! Many people find that simply reading, thinking or talking about yawning can trigger the reflex.
