Everyone yawns — when they're tired, bored, or simply watching someone else do it. Yet scientists still don't fully agree on why this strange, involuntary reflex exists.
Here's what research actually supports about yawning, its possible purposes, and why it seems to spread from person to person.
A yawn is an involuntary reflex involving a deep inhale, a brief hold, and an audible exhale, often paired with stretching.
Yawning occurs across the animal kingdom, including in mammals, birds, reptiles, and even some fish.
One long-standing theory holds that yawning helps regulate brain temperature by drawing in cooler air and increasing blood flow to the brain.
The idea that yawning simply raises blood oxygen or lowers carbon dioxide has been largely discredited by experiments showing people yawn at the same rate breathing pure oxygen as normal air.
Yawning is most common during transitions in arousal state, such as waking up, getting drowsy, or shifting from one activity to another.
Contagious yawning — yawning after seeing, hearing, or even reading about someone else yawning — occurs in humans starting around age four or five.
Researchers have found evidence of contagious yawning in chimpanzees, dogs, wolves, and even budgerigars (a type of parakeet).
A 2013 University of Tokyo study found dogs yawned more often after watching their owner yawn than after watching a stranger yawn, suggesting an emotional bond may play a role.
Whether contagious yawning is linked to empathy is still debated among scientists; some studies support the connection, while others find no clear link between empathy scores and yawn contagion.
Studies on whether women are more susceptible to contagious yawning than men have produced mixed results, with some finding a gender difference and others finding none.
People are more likely to catch a yawn from a close friend or family member than from a stranger, an effect researchers call the 'emotional bias hypothesis'.
Some research suggests people who score higher on psychopathic personality traits are less likely to yawn contagiously.
A developing fetus can yawn in the womb, though researchers are unsure whether this is a true yawn or a related reflex.
Excessive or unusual yawning can occasionally signal an underlying medical issue, such as sleep disorders or the side effects of certain medications — it's worth mentioning to a doctor if it's new or extreme.
A single yawn typically lasts about 6 seconds, and there's usually a short refractory period afterward before another yawn can be triggered.
Reading about yawning or even thinking about yawning can trigger the urge to yawn — this article is a good example.
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