Why We Really Yawn: It's Not for More Oxygen, It's to Cool Our Brains

Why do we yawn? The common belief is that yawning can help increase our oxygen supply. Yet now, scientists have found that this might not be the reason for yawning. Instead, we may yawn in order to cool our brains.

Previous research has actually failed to show an association between yawning and blood oxygen levels. That's why researchers decided to delve a bit further to see exactly what yawning may be used for instead.

Sleep cycles, cortical arousal and stress are actually all associated with fluctuations in brain temperature. Not only that, but yawning could potentially be used to keep the brain temperature balanced and in optimal homeostasis. In theory, yawning should be easily manipulated by ambient temperature variation, since exchange with cool ambient air temperature may facilitate lowering brain temperature.

In order to test whether yawning might be used to lower brain temperature, the researchers measured contagious yawning frequencies of pedestrians outdoors in Vienna, Austria during both the winter and summer months. They then compared their results to an identical study conducted in the arid climate of Arizona, USA.

So what did they find? It turns out that in Vienna, people yawned more in summer than in the winter. In Arizona, in contrast, people yawned more in the winter than in the summer. The scientists also discovered that contagious yawning was constrained to an optimal thermal zone or range of ambient temperatures around 20 degrees Celsius. This contagious yawning decreased when temperatures were high at around 37 degrees Celsius in the summer or low and around freezing in the winter.

The findings reveal that while yawning functions to cool the brain, this behavior is not functional when ambient temperatures are as hot as the body. This means that yawning may not be necessary or may even be harmful when it's too hot or too cold.

The findings are published in the journal Physiology & Behavior.