What Causes A Yawn?

By Marisa Ramiccio. May 7th 2016

What makes us yawn? Other people yawning, of course! At least, that’s what you may be thinking. But the contagious yawning theory is just one of many attempts to explain what causes a yawn. The truth is, the reasons why we yawn have yet to be scientifically proven. But many researchers have come up with some plausible answers that may turn out to be true.

Feeling Sleepy, Drowsy or Bored

When you find yourself yawning every few minutes at night, it’s a pretty good indicator that it’s time to go to bed. Yawning is a common response to sleepiness or drowsiness and yes, even boredom. That’s because when you are tired or bored, your breathing tends to slow down. As a result, your body tries to take in more oxygen by yawning. Some people believe that your body triggers a yawn to also get rid of the buildup of carbon dioxide, but research proves that this may not be true.

Dr. Robert Provine, a researcher at the University of Maryland, conducted studies on exercisers and found that increased oxygen and decreased carbon dioxide levels did not prevent yawning. Provine suggests that yawning may just be a behavioral response to a change in state such as a change from alertness to boredom or wakefulness to sleepiness. This coincides with other theories that suggest our circadian rhythms may signal our bodies to yawn as we become sleepier or more awake.

The Temperature of the Brain

When your brain is feeling overheated, it may yawn to cool itself down. Studies show that when outside temperatures and the inside temperatures of the brain coincide, yawning may be induced.

One study in particular showed that when people pressed a warm compress to their forehead, they were more likely to yawn than when they pressed a cold compress to their forehead. Those who breathed through their noses, which is said to cool the brain’s temperature, never yawned. If yawning does in fact cool the brain down, it can be beneficial: A cooler brain means that you can think more clearly.

Other People Yawning

One person yawns, then you yawn, then someone else yawns. The theory that yawning is contagious is an old one, but why does someone else yawning make us want to do the same thing? Some people say that it goes back to the carbon dioxide levels. Groups of people give off higher levels of carbon dioxide than just one or two people, so the chances of yawning are increased simply by being around a larger group. Others believe that contagious yawning is an evolutionary response leftover from the caveman days. This theory portends that people would use yawning as a signal; when one member of a group yawned, others would yawn back. Still others believe that it may have been a way to coordinate the behavior of a group of animals.

What has been established about the contagious theory is that the same area of the brain that’s responsible for empathy is responsible for yawning. So when you see someone else yawn, you may do the same out of empathy.

Excessive Yawning

Excessive yawning is more than a theory, it’s actually an indication of something more serious called a vasovagal reaction. The yawning occurs as a response to the vagus nerve, which is the longest cranial nerve. When this nerve acts upon the blood vessels, it causes the body to yawn. This is usually a sign of a heart problem to come such as a heart attack or an aortic dissection, which is a separation of the aortal walls. Aside from yawning, excessive daytime sleepiness is another warning sign of a vasovagal reaction. If you’ve experienced both of these symptoms, schedule a visit with your doctor to find out if you’re having a vasovagal reaction.

What Other Ways Does Yawning Benefit The Body?

So we know what may be the cause of yawning, but what are other reasons that yawning may benefit us? Here’s what some scientists believe:

  • It helps us stretch our muscles.
  • It can increase heart rate.
  • It can help us to feel more awake and alert.

Yawning may also be a simple reflex used to redistribute the amount of surfactant, which is an oily substance that lubricates the lungs and airways to prevent them from collapsing. If surfactant wasn’t redistributed, breathing would become more and more of a struggle.

Bottom Line

Although many theories and explanations as to why we yawn have been put forth, only one has survived the test of time: the contagious theory. It’s the most commonly known out of all of the theories and it’s the one that people tend to believe. To add to that theory, some researchers have suggested that just thinking about yawning can cause you to yawn – a psychosomatic response. In fact, you’ve probably yawned at least once or twice while reading this article.


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