Try reading this whole article without yawning. Chances are, somewhere around the second paragraph, you'll feel one coming. Yawning is one of the most common things the human body does, and one of the strangest. We do it when we're tired, when we're bored, before an exam, and, most mysteriously, when we see or even read about someone else doing it.
So why do we yawn? Scientists still haven't settled the question completely, but research over the past few decades has busted some old myths and produced a few surprising answers. Here's what science knows about yawning and why it is so contagious. Another odd body reaction with a real explanation: why music gives us goosebumps.
What Is a Yawn?
A yawn is an involuntary reflex: a long, deep breath in with the mouth wide open, a stretch of the jaw, often a stretch of the whole body, and then a shorter breath out. A typical human yawn lasts around six seconds. During a yawn, your heart rate can rise, and the stretching muscles of the jaw and face push blood around the head.
Yawning starts remarkably early. Ultrasound studies have recorded babies yawning in the womb in the first half of pregnancy. And it is not just humans: almost all vertebrates yawn, including cats, dogs, lions, birds, reptiles and even fish.
Myth: We Yawn Because We Need More Oxygen
For a long time, the most common explanation was that yawning brings extra oxygen into the body when blood oxygen runs low or carbon dioxide builds up. It sounds logical, but the evidence doesn't support it.
In the 1980s, psychologist Robert Provine, a pioneer of yawning research, tested the idea by having volunteers breathe air with extra carbon dioxide or pure oxygen. Their yawning rate didn't change. Breathing extra oxygen didn't stop yawns, and extra carbon dioxide didn't cause more of them. Most scientists have since dropped the oxygen theory.
The Leading Theory: Yawning Cools the Brain
One of the best-supported explanations today is the brain-cooling hypothesis, championed by psychologist Andrew Gallup and colleagues. The idea is that a yawn works like a radiator for your head:
- The deep breath pulls in air that is usually cooler than body temperature.
- The big jaw stretch increases blood flow to the skull, carrying away heat.
- Together, these may help bring the brain back to its ideal temperature, which helps keep you alert.
Several experiments back this up. People tend to yawn more when the outside temperature is moderate and less when it is very hot (when breathing in air wouldn't cool anything) or very cold. In one study, volunteers who held a cold pack to their forehead yawned less while watching videos of other people yawning than those holding a warm pack. Research by Gallup's team also found that across many mammal species, animals with bigger, more complex brains tend to have longer yawns.
The cooling idea also fits the moments when we yawn most: when we are sleepy, waking up, or bored, all times when the brain may be running a little warm or sluggish and needs a nudge toward alertness. That's also why athletes, paratroopers and students often yawn before a big moment. It may be the body's way of sharpening attention, not a sign of boredom.
Why Is Yawning Contagious?
Seeing someone yawn, hearing a yawn, or even thinking about yawning can set you off. This is called contagious yawning, and it is surprisingly powerful. In Provine's experiments, more than half of the people who watched a video of others yawning yawned themselves within five minutes.
Scientists have several ideas about why it happens:
1. Social connection and empathy
Studies have found that people are more likely to "catch" a yawn from family and close friends than from strangers. That has led some researchers to link contagious yawning to empathy and social bonding, a way of unconsciously syncing up with the people around us.
2. A group alertness signal
Another idea builds on brain cooling. If one member of a group yawns to boost alertness, others copying the yawn could help the whole group stay alert together, which would have been useful for early humans watching for danger.
3. Automatic mimicry
Humans copy each other constantly without noticing: smiles, postures, accents. Brain imaging studies suggest that watching a yawn activates some of the same areas involved in imitating actions. Contagious yawning may be one of the strongest examples of this automatic copying.
The empathy link is still debated. A large study from Duke University in 2014 found that age was a better predictor than empathy scores: older people were somewhat less likely to catch yawns. The honest answer is that contagious yawning probably has more than one cause.
Who Catches Yawns, and Who Doesn't?
- Young children: Babies yawn from the start, but contagious yawning usually doesn't show up until children are around four or five years old, about the age when they get better at understanding other people's feelings.
- Not everyone: Even among adults, a fair share of people rarely or never catch yawns, and scientists aren't sure why.
- Dogs: Several studies suggest dogs can catch yawns from humans, especially from their owners. A dog yawning can also be a sign of stress, not just sleepiness.
- Other animals: Chimpanzees and bonobos catch yawns from each other, and some studies report contagious yawning in other social animals as well.
Is Too Much Yawning a Sign of Something Wrong?
Most yawning is completely normal. The most common reason for frequent yawning is simply not getting enough sleep. But yawning far more than usual, especially if it comes with dizziness, fainting, unusual tiredness or other symptoms, can sometimes be linked to medications or health conditions. If your yawning suddenly changes a lot, it's worth mentioning to a doctor.
If this week's clock change leaves you yawning all afternoon, our guide to fixing your sleep schedule after the clocks fall back can help. And if you like weird body science, don't miss what causes brain freeze or why cats purr.
Fun Facts About Yawning
- The average human yawn lasts about six seconds.
- Reading about yawning, like you are now, can be enough to make you yawn.
- Covering your mouth when you yawn has been considered polite for centuries in many cultures.
- Some species, such as snakes, yawn to realign their jaws after swallowing a big meal.
- Trying to hold back a yawn rarely works. The urge usually wins.
Yawns and plane ears have a link too. Yawning and swallowing can open the Eustachian tubes that connect your throat to your ears, which is why they often help when cabin pressure changes. For the pressure science and how to clear your ears, read why your ears pop on a plane.
Frequently Asked Questions
Why do we yawn when we're tired?
One leading theory is that yawning helps cool the brain and increase alertness. When you are tired, your body may yawn to help keep you awake and focused.
Do we yawn because we need oxygen?
Probably not. Experiments found that breathing extra oxygen or extra carbon dioxide does not change how often people yawn.
Why are yawns contagious?
Scientists think contagious yawning may be linked to social bonding, automatic mimicry and group alertness. People catch yawns more often from friends and family than from strangers.
Can dogs catch yawns from humans?
Several studies suggest they can, especially from people they know well.
How long does a yawn last?
The average human yawn lasts about six seconds.
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