What Is the Cause of Yawning?

Written by sarah rigg
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What Is the Cause of Yawning?
(Wikimedia Commons | Steve Evans)

Yawning is an action common to all human cultures and among many animal species, from cats and dogs to tigers and chimps. It's a well-known phenomenon that yawns are contagious--meaning if you see someone else yawn or even just read about yawning, it can cause you to yawn. Here, you'll learn about the various causes of yawning and what theories scientists have about why we yawn.

Tiredness and Stress

A common cause of yawning is feeling tired, sleepy or stressed. Dr. George A. Bubenik of the University of Guelph in Ontario says the presence of certain brain chemicals such as serotonin and dopamine make us more likely to yawn. Conversely, the presence of other brain chemicals, including endorphins, makes us less likely to yawn. Being tired, stressed or tense tends to increase the yawn-producing brain chemicals and lower the level of endorphins. Another theory is that we yawn upon waking and at bedtime because yawning is a mechanism for helping us make transitions from one state to another.


Even when they're well rested, some people find that they yawn when they are bored. Yawning from boredom may also be linked to brain chemicals, since we seldom feel bored when we have a rush of endorphins in the body. Yawning is thought by some researchers to be our body's way of not only waking us up but helping us achieve a focus of attention--just the opposite of the wandering state of mind we experience when we're bored.

"Contagious" Yawning

The idea that yawns are contagious is not just folklore or myth--scientific studies have shown that the phenomenon is real. In humans, this may be because we are social creatures and tend to emulate those around us. When we see others yawning, we are prompted to yawn ourselves. Modern theories about "mirror neurons" may play a role, too. Our mirror neurons are cells in our brain that regulate us noticing when we're being copied and influencing us to copy others, whether it's returning a smile for a smile or yawning when we see someone else do it.

Modern Theory: Yawns Cool the Brain

In the past, scientists theorised that yawning helped wake you up because it sent extra oxygen to the brain. However, observational studies found that levels of oxygen or carbon dioxide in the bloodstream don't affect how likely we are to yawn. Instead, in 2007, University at Albany researchers conducted a study which suggest that yawns help cool the brain and keep it from "overheating." In part of the experiment, subjects who held cold packs to their foreheads were less likely to yawn than those who had warm or room-temperature packs. They concluded that a cooler brain runs more efficiently and is better able to focus.

Yawning in Animals

Though many mammals yawn, the reasons they yawn might be different than the reasons humans do. Research has shown that chimpanzees--highly social primates not unlike humans--experience contagious or mimicking yawns. Other species, notably baboons, may use yawns as a show of intimidation, since yawning bares their teeth to a rival.

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