There is a reasonable chance that simply reading an article about yawning will make you yawn.
If it happens, apologies.
Also: science would quite like an explanation.
Yawning is an ancient behaviour found across numerous animal species. Humans do it when tired, bored, waking up and sometimes simply because somebody else did it first.
Researchers have proposed explanations involving oxygen, alertness, brain temperature and social communication.
The awkward part?
There still isn’t one universally accepted explanation for why yawning exists.
No, You Probably Aren’t Yawning Because You Need More Oxygen
One of the oldest popular explanations is that yawning helps the body take in extra oxygen or get rid of excess carbon dioxide.
It sounds beautifully sensible.
Big breath. More oxygen. Problem solved.
Unfortunately, experiments have failed to provide convincing support for that simple explanation.
Changing oxygen and carbon dioxide levels does not reliably cause yawning to behave as the theory predicts.
So although a yawn obviously involves taking a large breath, breathing itself does not appear to be the whole reason the behaviour evolved.
Yawning Seems Connected to Changing States
One thing researchers do know is that yawning commonly appears during transitions in alertness.
People often yawn shortly before sleeping, after waking, when bored or during periods when attention is changing.
That has led to proposals that yawning may have something to do with regulating arousal or helping the brain shift between states.
Another prominent idea is thermoregulation.
Some researchers have found evidence consistent with yawning helping regulate brain temperature, including changes in yawning behaviour under different environmental temperatures.
The idea is intriguing, but it remains debated.
And that is basically the recurring theme of yawning research: several explanations have interesting evidence behind them, but yawning stubbornly refuses to hand scientists one neat answer.
Then Contagious Yawning Makes Everything Weirder
Spontaneous yawning is strange enough.
Contagious yawning adds another layer.
Seeing someone yawn can trigger a yawn in another person. Hearing one can do it. Thinking or reading about yawning may occasionally be enough.
Brain-imaging research has shown that observing yawns activates regions involved in processing social cues.
Contagious yawning has also been observed in some other animals.
So perhaps yawning is partly social.
One proposal is that contagious yawning helps synchronise states within a group. If one individual is becoming tired, alert or changing activity, spreading the behaviour might help coordinate everyone else.
There have also been suggestions that contagious yawning is linked to empathy.
That idea became extremely popular.
The scientific evidence, however, is much messier.
Is Contagious Yawning Really a Sign of Empathy?
Not reliably.
Some studies have found associations between social familiarity, aspects of social cognition and the likelihood of catching a yawn.
But reviews of the evidence have concluded that the claim that contagious yawning directly measures empathy is not well established.
In other words, failing to yawn when somebody else does is not evidence that you are secretly a monster.
Attention, age, individual differences and the situation itself can all affect whether yawning spreads.
Researchers know that contagious yawning is real.
Exactly why it happens is another question.
Why Can Reading About Yawning Make You Yawn?
If you have yawned somewhere during this article, you are providing an annoyingly convenient demonstration.
Contagious responses do not necessarily require watching a real person yawn in front of you.
Visual cues, sounds and even thoughts associated with yawning can sometimes be sufficient.
The brain is remarkably good at activating responses from cues associated with actions and sensations.
Once your attention has been repeatedly directed towards yawning, the threshold for actually performing one may become easier to cross.
Or perhaps you were tired anyway.
Yawning researchers have learned to live with ambiguity.
The Bottom Line
Yawning is extremely old, widespread and easy to recognise.
What it is actually for is still surprisingly difficult to pin down.
Ideas involving changes in alertness, thermoregulation and communication all have evidence behind them, while the old “your body needs more oxygen” explanation has not held up well.
Contagious yawning is definitely real, but even there, the popular claim that it is simply a measure of empathy goes further than the evidence allows.
So humanity has mastered powered flight, split the atom and landed machinery on other planets.
But apparently we still cannot completely explain why somebody opening their mouth makes everybody else want to do the same thing.
FAQ
Why do humans yawn?
There is no single universally accepted explanation. Yawning appears linked to changes in alertness and may have physiological and social functions.
Do we yawn because we need more oxygen?
The traditional oxygen explanation has not been well supported by experimental evidence.
Why are yawns contagious?
The precise mechanism remains uncertain. Research suggests that attention and social processing are involved, but there is no single confirmed explanation.
Does catching yawns mean you are empathetic?
Not necessarily. Although researchers have investigated a possible connection, reviews have found the evidence linking contagious yawning directly to empathy is inconsistent.
Further Reading
Why Does Your Voice Sound So Weird in Recordings? There’s a Physical Reason
Why Do You Get Goosebumps? Your Body Is Running Ancient Software
Why Do You Forget Why You Walked Into a Room? The Doorway Might Actually Be Part of It
Sources
Why do we yawn? :: https://pubmed.ncbi.nlm.nih.gov/20382180/
Why contagious yawning does not (yet) equate to empathy :: https://pubmed.ncbi.nlm.nih.gov/28735879/
Yearning to yawn: the neural basis of contagious yawning :: https://pubmed.ncbi.nlm.nih.gov/15670705/
The thermoregulatory theory of yawning: what we know from over 5 years of research :: https://pubmed.ncbi.nlm.nih.gov/23293583/