Why Are Yawns Contagious? The Sleep Science Behind the Phenomenon

People seem to yawn around us all the time. That’s nothing new. We assume it has something to do with what our teachers used to tell our parents at parent/teacher conferences. Something about “underdeveloped interpersonal skills” and “incredibly awkward social techniques.”

Here’s the thing… Whenever we see other people yawn, we feel compelled to join in. Since people are always yawning in our presence, we find ourselves perpetually mimicking them, even when we don’t feel particularly tired.

Is yawning contagious? Is there some kind of weird sleeping sickness going around that we should know about? Could this be a flare-up of the largely-forgotten epidemic of the early 20th century that left people in a horrifying zombie-like condition?

Let’s dig into the phenomenon that suggests that yawning is contagious and find out whether it really is.

The Big Question: Why Do We Yawn?

Yawning: the universal signal for “I’m bored,” “I’m tired,” or, occasionally, “Your lecture is fascinating, really.” The average adult yawns about 20 times a day, and if you’re anything like us, just reading that sentence might have you stifling one right now. Go ahead, let it out. We won’t judge. But why, exactly, are yawns so irresistibly contagious? Why does seeing someone yawn—or even thinking about yawning—trigger a chain reaction that’s one part science and one part mystery?

We’ve consulted the experts—a speech scientist, a neurologist, a neuroethicist, and a neuroscientist who also dabbles in itch studies (yes, that’s a thing)—to unravel the science behind yawning and its pesky, contagious nature.

Here’s the kicker: no one really knows. Despite yawning being as old as time—or at least as old as the first sleepy caveman sitting through an 8:00 a.m. Calculus class — it remains one of biology’s enduring mysteries.

Theory 1: Yawning is a Breathing Super Power

One popular theory, according to Douglas Parham, a speech scientist at Wichita State University, is that yawning is a special kind of respiration. When we’re tired or bored, we stop taking those nice, deep breaths. The result? A build-up of carbon dioxide in the body. A yawn might be the body’s dramatic way of saying, “We need oxygen, stat!” By yawning, we get a supercharged gulp of oxygen while expelling excess carbon dioxide. It’s like hitting the refresh button on your lungs.

Theory 2: Brain Chemistry and a Facial-Muscle Squeeze

But that’s not all. James Giordano, a neuroethicist at Georgetown University, suggests yawning might also be triggered by chemical changes in the brain, such as an increase in carbon dioxide or adenosine (a compound linked to drowsiness). By compressing facial muscles during a yawn, we might be helping to send oxygen-rich blood zooming to the brain. It’s certainly more efficient than having to compress your head in a vice whenever you need an O₂ hit.

Other Ideas

Other theories? Yawning might cool down the brain (because even brains need AC), stretch out internal organs, or just give our body a much-needed wake-up call.

What About Animal Yawns?

Humans don’t have a monopoly on yawning. According to Thomas Scammell, a neurologist at Harvard Medical School, yawning is a primitive reflex that starts in the brain stem—a region we share with birds, reptiles, and even some sharks.

Most mammals yawn. Cats do it. Dogs do it. Even hippos do it, and we’d argue they do it with the most flair. Curiously, the contagious nature of yawning seems to jump from one species to another. Just watch a video of a lion yawning as it sprawls lazily in the sun and tell us you don’t feel the urge to mimic the behavior.

Fun fact: animals with bigger brains tend to yawn longer. Keep that in mind the next time your teenage yawns while being lectured about not knowing enough. This supports the idea that yawning might be tied to brain chemistry. Still, scientists aren’t entirely sure why yawning exists in the first place, let alone why animals like sharks get in on the act.

The Domino Effect: Why Are Yawns Contagious?

Now for the pièce de résistance: why does one yawn lead to another? Studies such as this one show that seeing someone yawn makes you six times more likely to yawn yourself. So, what gives?

James Giordano says it might boil down to social mirroring, a phenomenon where we unconsciously mimic the actions of those around us. Think of it as the brain’s version of peer pressure. Yawning falls into the same category as scratching, laughing, and, apparently, crossing your legs at the same time as the person sitting next to you.

This mirroring behavior might be linked to mirror neurons—brain cells that fire when we see someone else perform an action. It’s the same mechanism that makes us wince when we see someone stub their toe. If your brain sees someone yawning, it thinks, “That looks like a great idea!” and before you know it, you’re yawning too.

It’s not just humans, either. Zhou-Feng Chen, director at Washington University’s Center for the Study of Itch, showed a video of a mouse scratching itself to other mice. Within five seconds, the onlookers started scratching too. Chen’s theory? Animals mimic behaviors they instinctively recognize as useful. In the wild, if one animal starts scratching, it might be a sign to the group that parasites are afoot. Yawning, like scratching, could be a way to stay in sync with the group and alert to potential threats.

The Social Side of Yawning

Yawning isn’t just about oxygen, carbon dioxide, or brain cooling—it’s also a subtle form of social bonding. Scammell explains that behaviors like yawning, smiling, or laughing back at someone who’s laughing are ways to build connections.

People who are more empathetic tend to catch yawns more easily, which might explain why your dog sometimes yawns when you do. (Yes, dogs can “catch” yawns from humans!) It’s all part of our brain’s way of saying, “Hey, we’re in this together.”

So, the next time someone accuses you of starting a yawn epidemic, tell them you’re just strengthening social bonds. After all, science says so.

Now, if you’ll excuse us, we’re tired of suppressing this yawn. Don’t take it personally. It has nothing to do with the pleasure of your company.

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