Why we yawn and what it means

Causes

Current research does not provide a definitive reason for yawning. However, researchers have proposed and studied many theories, which provide some clues.

A change of state

People commonly consider yawning a sign of sleepiness or boredom, though this is not always the case.

While someone who yawns may be tired, the heart rate quickly rises during a yawn. This increased heart rate suggests yawning can be a sign of alertness rather than sluggishness.

Yawning, in general, may simply be a way for the body to change the state of awareness it is in:

• Before bed: yawning could be taken as a sign that the body is preparing for sleep.
• When bored: yawning while doing a boring task may be a sign of the brain transitioning from a high level of alertness to a lower one.

People may also yawn when changing physical states, such as moving from an area of high pressure to low pressure. This pressure can build up in the eardrums and may cause the person to yawn to release it.

A respiratory function

Yawning may serve a function related to breathing. Yawns may be more likely to occur when the blood needs oxygen. A yawn causes a big intake of air and a faster heartbeat, which could theoretically mean it is pumping more oxygen through the body. So, a yawn may function to expel carbon dioxide from the blood while providing a fresh oxygen supply.

One 2022 study supports this physiological function of yawning. The study claims that yawning is a critical behavior for maintaining airway health and function, with implications for respiration, sleep, and muscle balance. However, the authors note that their study has limitations and that further research is necessary.

To cool the brain

Yawning may cool the brain. A yawn causes the jaw to stretch out, increasing blood flow in the face and neck. The large inhalation and rapid heartbeat caused by the yawn also cause blood and spinal fluid to cycle through the body faster. This process may be a way to cool down a brain that has gotten too hot.

A 2021 study supports this hypothesis by relating yawning frequency with brain mass. Researchers analyzed yawning in over 100 animal species and found that those with larger brains and more neurons tend to yawn for longer. They suggested that longer yawns help cool bigger brains, which generate more heat.

However, researchers need to conduct more studies to confirm whether yawning in humans serves primarily to cool the brain or if other factors play a larger role.

As a communication tool

Some researchers believe the reason humans yawn has more to do with evolution. Before humans communicated vocally, they may have used yawns to convey a message.

Yawns are considered a sign of boredom or sleepiness, which could also be what early humans were communicating to each other. However, early humans may have used yawning to signal their alertness to others, bare their teeth to aggressors, or serve as some other communication tool.

Yawning in other animals

Humans and chimpanzees are not the only animals that yawn. All vertebrates, from fish and birds to wolves, and horses, yawn.

According to a 2022 study, contagious yawning has been observed in humans and at least nine other species, such as chimpanzees, wolves, and dogs.

However, the authors note that their study has limitations and that further research on this topic is necessary.

Why is yawning contagious?

Yawning is a reflex that does not follow many consistent patterns.

One thing that many people agree on is that yawning appears to be contagious. Seeing another person yawn can cause those watching to “catch” the yawn themselves.

Science has wondered why this happens, and many theories have surfaced, including:

• Time of day: Some researchers have suggested that the time of day or the intelligence of the people who catch the yawn causes contagious yawning. However, this theory has lost traction in recent years.
• Empathy: One of the most common theories is that contagious yawning is a sign of empathy for others. Seeing a person yawn may cause the viewer to yawn, especially if they are close to or comfortable with that person.

One 2022 study investigating yawning contagion in red-capped mangabey monkeys discovered they yawned more often when they saw yawning, whether from other mangabeys or humans. Researchers concluded that familiarity and social bonds played a key role, with the monkeys yawning more in response to yawns from familiar individuals than unfamiliar ones.

Conversely, another 2022 study found the yawn response was not significantly influenced by how closely related or familiar the species was to humans. This contradicts the idea that empathy or emotional connection plays a role. Rather, they found that humans can yawn contagiously in response to yawns from non-human animals, showing the first evidence of interspecies contagious yawning.

Ultimately, researchers need to conduct more studies on this complex topic.

Can one yawn too much?

Yawning is usually harmless, but it is possible to yawn too much. A few disorders that require medical attention can cause excessive yawning.

The vagus nerve, which iconnects the throat and abdomen to the brain, can cause excessive yawning by interacting with the blood vessels. This is called a vasovagal reaction. This response may be a sign of a sleep disorder or brain condition. It can even be a sign of heart conditions, such as a heart attack or bleeding around the heart.

If excessive yawning occurs without apparent cause, a person should contact a medical professional.

Summary

Yawning remains a fascinating and complex behavior that appears to involve a combination of physiological, psychological, and social elements. However, researchers have yet to agree on a definitive cause.

Though typically harmless, excessive yawning may signal an underlying health issue. If a person is concerned about this, they should talk with their doctor.