Why Do We Yawn?

Published: 11 February, 2025 | 6'

Did you know that humans yawn around 20 times a day? Normally, this involuntary act is associated with tiredness or sleep, but nowadays there is no scientific evidence that provides a conclusive explanation for why it occurs. In fact, reading this article might even make you feel the urge to yawn.

We will tell you about the different theories that exist on the subject and the various common situations in which yawning occurs.

What is a yawn?

The act of yawning occurs when we feel the need to involuntarily open our mouth to take a deep breath for about 5 seconds and then follow it with a brief exhalation. Not only do humans yawn, but other vertebrate animals do as well.

Characteristics of yawning: involuntary and contagious

Although in some cultures it is considered rude to do so in public, it is an involuntary act. We usually associate it with sleep or tiredness, as it happens more frequently in those situations, but it has also acquired other social characteristics, as it has been shown to be contagious.

There is a tendency to yawn after noticing that another person is yawning, and this is more common if we have a close emotional connection with that person. Furthermore, it can happen that the yawn is contagious merely by hearing that other person do it.

Main theories about yawning

There are several theories about why yawning occurs, many of which suggest that it is a gesture inherited from our ancestors, and that it serves as a communication system. For example, babies also yawn and begin to do so during gestation, which could signify that this act is a way for them to communicate with their parents before speech in humans, or through other gestures and patterns of behaviour in other animals.

Oxygenation theory

One theory posits that yawning occurs when blood or brain oxygenation levels are insufficient, thus yawning promotes oxygen supply to the blood. This may seem plausible, but studies have reported that high levels of oxygen do not influence the number of yawns, nor do we yawn more when in small spaces with higher levels of carbon dioxide.

Regulation of brain temperature

Another theory suggests that yawning helps control brain temperature. When we yawn, there is greater ventilation and airflow entering the body through the mouth. As such, usual tiredness after intense mental or physical activity raises brain temperature and increases the urge to yawn. This also explains how common it is to yawn before going to bed, as it reduces body and brain temperature, facilitating the onset of sleep.

Effect on attention

There is also a widespread belief that yawning can enhance attention capacity by restoring the appropriate temperature following an increase in brain temperature. Therefore, during activities that require attention, such as studying or working, yawning may boost mental performance to maintain focus. This could explain the belief that we yawn when we are “bored”, as it may be the brain's way of sustaining its activity during these situations. However, studies do not indicate any excitatory effect on the brain following yawning.

Empathy and social communication theory

The contagious nature of yawning finds its explanation in our brain, specifically in the so-called mirror neurons, which are related to empathy. These neurons activate when we see another person performing a gesture or behaviour, especially during childhood, as they are activated to learn to carry out any activity, even when learning to speak. Mirror neurons also activate when discussing this specific gesture and even when reading about it, which is why it is very likely that you have yawned several times while reading this article.

Although yawning is universal and everyone does it, the contagion does not follow a pattern, as not everyone becomes contagious when seeing someone yawn. Some theories suggest that proximity to the person increases the likelihood of contagion, for example, if they are a family member or friend. Others suggest that individuals with conditions affecting social interaction or personality, such as autism, seem to respond less to the contagious effect of any gesture because they tend to look less at the people around them, although there is no clear evidence on this matter.

What factors provoke yawning?

Yawning can occur throughout the day, and it is something we commonly do that we share with both humans and animals, although there are situations in which it is more common or associated with specific moments in our routine.

Physiological factors

The structures necessary to trigger the action of yawning are located in our brain, specifically in the medulla oblongata, from where signals are dispatched through excitatory amino acids, dopamine, and oxytocin. Other areas, such as the cerebellum and cerebral cortex, also play a role in yawning.

When we feel sleepy or tired, our breathing slows down. Thus, following some of the theories mentioned earlier, our brain might initiate this process to enhance attention and regulate neuronal activity. That is why it is common to yawn upon waking and also when preparing to go to bed.

Environmental factors

In monotonous situations or activities that are not engaging, we enter what is commonly known as “boredom”, which is essentially a lack of mental stimulation and nervous excitement. It is believed that yawning, by activating neuronal activity, occurs as a way to cope with this situation to stimulate oneself and maintain attention. In fact, when we are bored, brain activity and behaviour change, and we even become more creative and flexible in order to escape that situation and find an activity to occupy our time.

Social imitation

Following the empathy theory and due to mirror neurons, it is very common to yawn when we see or hear someone else do it. This is also linked to a hypothesis regarding our evolution, claiming that yawning was an ancient form of communication, similar to what occurs with babies who have yet to learn speech or other gestures. Moreover, contagious yawning has only been observed in humans, dogs, and chimpanzees.

Curiosities about yawning

Evidence regarding why yawning occurs is scarce and uncertain, although there are common patterns among all living beings that yawn. For example, it is an involuntary act that cannot be interrupted once the impulse has started. Additionally, if one tries to suppress or avoid it, it results in dissatisfaction.

Yawning during physical exercise

It is likely to feel the urge to yawn when starting physical exercise, and although there is no definitive evidence, this impulse may stem from an increase in body temperature, prompting the brain to send the signal to yawn and take in cool air to regulate temperature.

Why do babies and animals yawn too?

Practically all vertebrate animals yawn, and we do so throughout our lives. Despite the lack of consensus on the evidence clarifying the origin of this impulse, yawning can regulate brain temperature, being highly beneficial for both humans and animals. In fact, babies begin to yawn from the 12th week of gestation in the womb, which could imply that this involuntary act plays an important role at the brain level.

What happens if we yawn a lot in one day?

It is normal to yawn several times a day, although excessive yawning in a continuous manner can be a symptom of certain conditions.

There is no need to worry if on a particular day we yawn more than usual, but if it becomes a regular occurrence, it is advisable to consult a healthcare professional, as it may be linked to conditions such as insomnia, migraines, or other conditions. It could also be a result of certain substances and even excessive caffeine intake.

Thus, while yawning in public may be considered impolite, don’t worry if you feel the urge to do so, and remember that it is an involuntary act that is necessary for your brain.

If you want to learn more about how your body works…

References

Content reviewed by specialists in the Scientific Information area of MARNYS. This article is informative and does not replace consulting a specialist.