Why do we yawn? Scientists once believed it was a way to get extra oxygen to a sleepy brain. On the contrary, recent studies say we yawn to regulate body temperature -- specifically, to cool our brains. Research has shown that people yawn most often when the ambient air temperature hovers around a comfortable 68º F (20º C), but yawn less and less often as the heat reaches their body temperature and beyond. This jibes with the brain-cooling theory, since cool air will have the biggest cooling effect and body-temperature air will just match the brain's heat. Interestingly, very cold temperatures don't make you yawn more often, maybe because they would cool the brain too much. But why does your brain get hot in the first place? Brain temperature rises with sleep deprivation -- just like yawning does.
How Yawning Keeps Your Brain Cool
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Key Facts In This Video
Babies begin to yawn during the second trimester. It may have to do with proper brain development. 00:25
Scientists believe that yawning has developed as a way of cooling your brain. 00:40
Contagious yawning begins in children around age 4–5. This is also when empathetic behavior begins. 01:28