Why do we yawn?

Yawning is a normal and involuntary action. When we yawn, we open the mouth, take a deep breath in, and slowly exhale out. Afterwards, there is usually a feeling of satisfaction and comfort.

Yawning mostly happens before sleeping and after waking up.¹ It can usually lasts for about five seconds, and it goes together with other stress-releasing body movements such as stretching out the limbs.

Yawning is the most common, yet least understood human behavior.

What causes it?

Sleepiness

Sometimes it can be a sign of sleepiness and fatigue. Other times it can be a sign of boredom.

Boredom and sleepiness both cause drowsiness, which can end up triggering a yawn through our sleep system. Some studies have found that when chimpanzees yawn, it is during or after physical activity and other times, mostly when sleepy.²

Yawning helps make it easier to stay awake during states of sleepiness. It has many different effects on the body that increase overall arousal and mental clarity.¹

Social Empathy

Why do we yawn when someone else does? Many people believe that it is contagious. Science says this stems from empathy, or humanly care. For this reason, seeing a person yawn can trigger another person to do the same.

Many research studies have been done with people of all ages, ranging from toddlers to adults, to test this theory. They found that contagious yawning can be seen with anyone capable of social interactions.³ Individual brain scans also encouraged this idea – people’s yawning responses were noticed to be in the same regions of the brain that control empathy and social behavior.  

Historically, it was a social behavior and a way to communicate. Based on this fact, people with increased empathy, or awareness of other people’s mental states, are most susceptible to contagious yawning.³

For the brain

For many centuries it was believed that yawning works to increase oxygen to the brain. If we are experiencing a lack of oxygen or an abundance of carbon dioxide in the blood or brain, it can trigger yawning. It was thought that this action was helping remove the “bad” carbon dioxide air and replacing it with fresh oxygen.¹ However, new research suggests that this is in fact not true.  

Andrew Gallop from Princeton University has suggested that it cools down the brain and regulates it overall temperature.

The thermoregulation theory of yawning says that it is a part of maintaining the body’s core temperature.⁴ The brain cooling hypothesis is the idea that it cools down the brain. The brain is extremely sensitive to temperature, and like a computer, needs to be cooled down. Many research studies have looked into understanding this. They found that it is controlled by the hypothalamus, which is also the center for brain temperature control.

Yawning causes changes in blood circulation and an increase in heart rate. Physically, yawning produces a nice stretch in the jaw, head, neck, and face which helps blood flow to all those areas. One way heat is released from the brain is through blood flow. By increasing blood flow, yawning may then remove “hot” blood from the brain and give it cooler blood pulled from the lungs and limbs instead.⁴

Ear pressure

Sometimes yawning can relieve ear discomfort or hearing problems. People experiencing altitude changes, such as in an elevator or on an airplane, can quickly feel air trapped in the middle ear.¹ The “defense reflex” of the ear can be triggered in these situations which leads to a yawn, which can then correct the changes in ear pressure and relieve uncomfortable symptoms.  

Excessive yawning

Excessive yawning occurs more than once per minute. Although normally because of sleepiness or boredom, excessive yawning can be caused by serious underlying medical conditions.

What causes excessive yawning?

Causes of excessive yawning can include tiredness and fatigue, sleep disorders, side effects from certain depression and anxiety medications, and bleeding around the heart.⁵ Other less common causes can include brain tumors, epilepsy, heart attack, liver failure, or an inability to control body temperature.⁵

How is it treated?

After a medical exam, a doctor might diagnose excessive yawning as a sleep disorder or other underlying medical condition.

To treat different sleep concerns, keeping a regular sleep schedule, frequently exercising, and using breathing devices can help.

Talk to your doctor if you are experiencing excessive yawning.

References:

1. Gupta, S., & Mittal, S. (2013). International journal of applied & basic medical research, 3(1), 11–15. https://doi.org/10.4103/2229-516X.112230

• Rossman, Z. T., Padfield, C., Young, D., Hart, B. L., & Hart, L. A. (2020). Frontiers in veterinary science, 7, 252. https://doi.org/10.3389/fvets.2020.00252

• Gallup A. C. (2021). Neuroscience and biobehavioral reviews, 121, 18–19.

https://doi.org/10.1016/j.neubiorev.2020.11.023

• Gallup AC, Eldakar OT. Front Neurosci. 2013;6:188. Published 2013 Jan 2. doi:10.3389/fnins.2012.00188

• Teive, H. A. G., Munhoz, R. P., Camargo, C. H. F., & Walusinski, O. (2018). Arquivos de Neuro-Psiquiatria, 76(7), 473–480. https://doi.org/10.1590/0004-282×20180057

Image by Sammy-Williams from Pixabay