Why Do We Yawn When Someone Else Yawns?

Have you ever watched someone yawn, only to find yourself doing the same thing a few seconds later? Sometimes, another person does not even need to be present. Hearing a yawn, watching one on a screen, imagining the action, or simply reading about it can be enough to create the urge.

Science calls this contagious yawning. But nothing is truly being transmitted from one person to another. What spreads is not air, germs, or a lack of oxygen. It is an automatic response created by the brain when it observes someone else’s behavior.

Spontaneous yawning and contagious yawning are not quite the same. Spontaneous yawning occurs without an outside trigger, often as we wake up, approach sleep, become bored, or remain inactive for a long time. Contagious yawning begins after we see, hear, or even think about someone else yawning. The movement is the same, but the triggers are different.

What makes a yawn contagious?

When we observe another person moving, the brain does more than passively watch. To understand the action, it begins to represent or quietly rehearse that movement within its own motor system.

This happens in many ordinary situations. We may tense our body while watching an athlete fall, soften our expression when speaking to someone who is smiling, or unconsciously adjust our speaking pace to match the person in front of us. When we see a yawning face, the motor systems involved in moving the jaw, face, and respiratory muscles also begin preparing the same action. If the resulting urge becomes strong enough, we yawn too.

People recognized the contagious nature of yawning long before scientists began studying it, so there is no single person who can be credited with discovering it. One of the pioneers of its modern scientific study, however, was the American neuroscientist Robert Provine.

In 1986, Provine showed people images of others yawning and also asked them simply to think about yawning. Both situations could trigger the behavior. His experiments demonstrated that yawning is not only a personal response to tiredness; it can also be set in motion by an observed or imagined action.

In a later study conducted in 2017, researchers measured the balance between excitation and inhibition in the motor cortex, a part of the brain involved in controlling movement. People whose motor systems were more easily excited were also more susceptible to contagious yawning. This may partly explain why the same image can make one person yawn immediately while leaving another completely unaffected.

Contagious yawning is often attributed to mirror neurons brain cells that respond both when we perform an action and when we observe someone else performing it. Mirror mechanisms may contribute to the process, but scientists have not proven that they are solely responsible. Brain-imaging studies suggest that contagious yawning involves several systems related to movement, attention, face perception, and behavioral control. There is no single “yawn button” in the brain.

Why do we open our mouths so widely?

A yawn is not simply an unusually deep breath. It is an automatic sequence of movements initiated by the brain and carried out in a fairly consistent order.

The jaw opens widely as the muscles of the face, jaw, and throat stretch. A long, deep inhalation follows. The movement reaches a brief peak before the muscles relax, air is released, and the mouth closes. Sometimes the neck, arms, and back stretch at the same time.

Opening the mouth so widely allows the muscles around the jaw, face, and upper airway to stretch forcefully. The lungs also expand much more than they do during an ordinary breath. The brief sense of relief that follows a yawn may come partly from these muscles tightening and then relaxing.

Yet the exact biological purpose of the entire movement remains uncertain. Yawning may affect several processes at once, including the opening of the airways, the regulation of alertness, and the control of brain temperature.

Do we yawn because we need more oxygen?

One of the most common explanations for yawning is that it helps the body take in more oxygen. Experiments, however, do not support this idea.

In 1987, Provine and his colleagues asked participants to breathe pure oxygen and air containing different concentrations of carbon dioxide. Although these changes affected breathing, they did not significantly alter how often people yawned. Exercise, which increases breathing rate, did not eliminate yawning either.

The fact that we inhale deeply during a yawn does not necessarily mean that a lack of oxygen caused it. Breathing and yawning appear to be controlled by different internal conditions.

A more strongly supported possibility is that yawning helps regulate brain temperature. According to this theory, the powerful movement of the jaw and facial muscles changes blood flow around the head, while the deep inhalation may help bring cooler blood toward the brain. Some experiments have found that cooling the head can reduce yawning and that yawn frequency changes with the surrounding temperature.

Studies comparing different animal species have also found that species with larger brains and more neurons tend to yawn for longer periods. These findings support the brain cooling theory, but they do not prove that cooling is the sole purpose of yawning. The behavior may perform several functions at once.

Why do we feel sleepy after yawning?

Yawning does not usually make us sleepy. More often, we yawn because we are already becoming sleepy.

Yawning frequently appears when the brain is moving from one state of alertness to another. We yawn as we approach sleep, but we also yawn shortly after waking. If the only purpose of yawning were to prepare us for sleep, yawning in the morning would make little sense.

Instead, yawning may accompany the transition between sleeping and waking. Some researchers believe it could briefly increase alertness when our level of arousal begins to change.

The physical relief that follows a yawn can also be confused with sleepiness. The jaw, face, and sometimes the entire body stretch before the muscles relax again. That release can feel calming, especially when we are already tired. Yawning and sleepiness are therefore often two results of the same change in the brain rather than one directly causing the other.

Are we born with contagious yawning?

Humans begin yawning before birth, which means spontaneous yawning is an ancient, inborn behavior. Babies and very young children, however, generally do not respond to another person’s yawn in the same way adults do.

Contagious yawning develops during early childhood and becomes more apparent at around four or five years of age. This is also a period when children’s understanding of other people’s faces, actions, and emotions becomes more advanced.

The difference suggests that yawning itself is innate, while catching a yawn depends on developing the ability to notice another person’s behavior and translate it into a response within one’s own motor system.

Is contagious yawning a sign of empathy?

Contagious yawning is often described as a sign of empathy. There is some evidence behind this idea, but the relationship is not as simple as it is sometimes presented.

In a 2011 study, 109 adults were observed in their everyday social environments over roughly one year. After examining hundreds of yawning episodes, researchers found that yawns spread more readily and quickly between relatives and close friends than between strangers. This suggested that emotional closeness might strengthen the response.

A larger study conducted in 2014, however, produced a more complicated picture. Researchers showed yawning videos to 328 people and compared their responses with measures of empathy, tiredness, cognitive performance, and time of day. None of these factors strongly explained who yawned and who did not.

Age was the only factor that showed a noticeable relationship: susceptibility to contagious yawning decreased slightly as people grew older. Even age explained only a small portion of the differences between individuals.

Failing to catch a yawn does not mean that someone lacks empathy, just as yawning easily is not proof of exceptional empathy. Emotional closeness may matter, but we may also be more attentive to people we know well, making us more likely to notice and respond to their behavior.

Do animals catch yawns too?

Contagious yawning is not exclusive to humans. It has been observed in chimpanzees, bonobos, some monkeys, dogs, wolves, lions, and several other social animals. The evidence is not equally strong for every species, however, and not all social animals appear to catch yawns.

This uneven distribution offers a possible clue about why contagious yawning evolved. It may help members of a group synchronize their periods of rest, alertness, and movement.

In one study of wild lions, animals that responded to another lion’s yawn with a yawn of their own were more likely to coordinate their subsequent movements. A change in one animal’s state could therefore spread through the group, helping its members rest or become active at similar times.

A comparable function may once have helped human groups coordinate their behavior. Still, scientists do not yet know whether synchronization is the original or only evolutionary purpose of contagious yawning.

What we can say with confidence is that seeing another person yawn causes the brain to prepare the same movement within our own body. If the urge becomes strong enough, we repeat the action. Why this response is much stronger in some people than in others and precisely what advantage it offered during evolution remains unresolved.

Perhaps that is what makes contagious yawning so intriguing: before we consciously decide to do anything, the body is already observing the people around us and, sometimes, quietly joining them.

References

1. Provine, R. R. (1986). Yawning as a Stereotyped Action Pattern and Releasing Stimulus. Ethology, 72, 109–122.

2. Provine, R. R., Tate, B. C., & Geldmacher, L. L. (1987). Yawning: No Effect of 3–5% CO₂, 100% O₂, and Exercise. Behavioral and Neural Biology, 48(3), 382–393.

3. Brown, B. J., et al. (2017). A Neural Basis for Contagious Yawning. Current Biology, 27(17), 2713–2717.

4. Norscia, I., & Palagi, E. (2011). Yawn Contagion and Empathy in Homo sapiens. PLOS ONE, 6(12).

5. Bartholomew, A. J., & Cirulli, E. T. (2014). Individual Variation in Contagious Yawning Susceptibility Is Highly Stable and Largely Unexplained by Empathy or Other Known Factors. PLOS ONE, 9(3).

6. Gallup, A. C., & Gallup, G. G. (2007). Yawning as a Brain Cooling Mechanism. Evolutionary Psychology, 5(1).

7. Massen, J. J. M., et al. (2021). Brain Size and Neuron Numbers Drive Differences in Yawn Duration Across Mammals and Birds. Communications Biology, 4.

8. Casetta, G., Nolfo, A. P., & Palagi, E. (2021). Yawn Contagion Promotes Motor Synchrony in Wild Lions. Animal Behaviour, 174, 149–159.