March 31, 2026
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In addition to signaling tiredness, yawning may also help carry cerebrospinal fluid away from the brain to help cool it down, a recent study suggests.
It's hard not to take other people's yawns personally, especially when you're in the middle of telling them a story.
Longstanding beliefs, and evidence, suggests that drowsiness, which often follows boredom, is a common stimulus for yawning. Also, when people yawn, heart rate increases and certain muscles in the face tense and stretch, possibly to alert the brain to wake up.
“We can think of the gaping of the jaw as a localized stretch, similar to stretching muscles in other areas of the body,” Andrew Gallup, a professor in behavioral biology at Johns Hopkins University, told the Guardian last year. “In the same way that stretching helps circulation in those extremities, yawns seem to do the same for the skull.”
Humans yawn, even in utero, as do animals ranging from baboons to parakeets.
But all of the reasons why people yawn, and the possible physiological benefits of it, are still not fully understood.
A recent study found that when people yawn, cerebrospinal fluid – which cushions the spine and brain – moves away from the brain. This process may cool down the brain and help remove metabolic waste from the body, the researchers said.
But the results were preliminary and the study was a small one, so more research is needed to verify these findings.
Another theory is that spontaneous yawning activates the parasympathetic nervous system, signaling the body to shift into "rest and digest" mode after a stressful period. In this way, yawning may help reduce anxiety.
And, yes, yawning is contagious.
The tendency people have to yawn after they see someone else do it may be an empathetic response serving another evolutionary purpose, Dr. Christian Agudelo, a neurologist at the University of Miami, said last year.
"If yawning occurs in preparation of a change in activity level, from low to very high activity, we should be aware when that is happening around us," Agudelo said. "A child would empathically yawn when their parent yawns because something is about to happen that is important. They are about to enter sleep or exit sleep, which are moments of greatest vulnerability.
"For early humans and animals, they may need to transition from sleep to action immediately. If a child sees that yawn and empathically yawns themselves, they are more likely to learn from the behaviors their parents take to survive the impending attack."
