When someone nearby yawns, we often feel as if we’ve lost bodily control. Our jaws open involuntarily, overcome by some unseen force and compelled to mimic the gaping mouth in our midst. Merely thinking about yawning can cause you to yawn — an unrelenting problem for anyone pondering and writing about the subject.

No one knows for sure what triggers this automatic (and often unconscious) response, but experts have proposed a few theories. Whether simultaneous yawning raises our collective awareness or strengthens our social connections, it certainly seems that the behavior is infectious.

What Causes Yawning?

To understand why we find yawning so contagious, it’s important to consider what causes yawns in the first place. For such a common phenomenon — the healthy average is up to 20 times per day — yawning remains somewhat mysterious. So what does yawning do?

One hypothesis is that yawning is simply your brain’s way of regulating its internal temperature. Studies have shown that a warm pack held to the forehead induces more frequent yawns than a cold one, suggesting they help your noggin cool down.

Another hypothesis is that yawning heightens alertness, which makes intuitive sense considering we typically do it during behavioral transitions — between sleeping and waking, between sitting around and getting active. Some researchers suggest that the way it contorts your face and neck may stimulate the carotid artery, raising your heart rate and jolting you to attention.

All of this can happen while you’re by yourself, of course. When a yawn isn’t triggered by someone else’s, it’s called a spontaneous yawn. But this garden variety reflex doesn’t usually pique our interest. What baffles us is the contagious yawn, with its strange ability to overpower us.

Read More: Why Do We Yawn?

Is Yawning Contagious?

So, why do we yawn in response to another person? It could be an evolutionary adaptation to synchronize group behavior. Imagine a band of prehistoric humans, keeping watch through the night against predators and foes. If one of them starts to doze off, it’s likely the rest are getting sleepy as well. When the first person yawns, that cue prompts everybody else to do the same, raising the group’s overall vigilance and safety.

Some research also points to a link between contagious yawning and empathy, the capacity to understand and share the emotions of another person (an essential trait for a species like Homo sapiens, with our complex social interactions). In support of this link, a 2020 study found that people are more likely to catch the contagion among family and friends. The deeper the bonds, the deeper the yawns, the study suggested.

Skeptics note, however, that a yawn doesn’t necessarily transmit the emotion that inspired it, perhaps undercutting the empathy hypothesis. As psychologists Jorg Massen and Andrew Gallup wrote in a paper from 2017, “it seems rather unlikely that people suddenly become bored when they see someone yawn as a result of uninteresting stimuli, or stressed when sensing yawns elicited by anxiety-provoking situations.”

Read More: Why Are Emotions Contagious?

Skeptics Question Just How Contagious Yawning Is

Whatever its purpose, contagious yawning certainly seems tied to big brains, and to sociality. Though many animals — from birds to fish to reptiles — have been caught agape, only highly intelligent, highly social species such as primates yawn as a reaction to their peers. In 2022, researchers found that humans even yawn in response to yawns from other animals.

Given that the yawning contagion is limited to the most intelligent and social creatures, it seems natural to connect it to their well-developed cognitive architecture. Though the evidence has been inconsistent so far, one theory holds that contagious yawning is the product of mirror neurons, copycat brain cells that fire both when we carry out an action ourselves and when we see someone else do it.

Beyond these theories, it’s worth noting that some researchers question whether yawns really are contagious. Psychologists Rohan Kapitány and Mark Nielsen have suggested that even if they aren’t, our knack for pattern recognition and confirmation bias could lead us to the wrong conclusions — we notice the few cases where yawns seem contagious and miss the far more numerous cases where yawns occur spontaneously. “We may have been doing little more than seeing faces in clouds or reading tea-leaves,” they wrote in 2017.

According to Kapitány and Nielson, additional research, with more creative and contentious methodologies, is needed to determine how contagious yawning really is, if it is contagious at all. How many yawns are spread in the course of that research, well, that’s something only time will tell.

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