十万个为什么·科学启蒙30篇（2）

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我们为什么会打哈欠？

Yawning is a reflex involving deep inhalation, stretching of jaw muscles, and often a slow exhalation — but its exact purpose remains debated.
One widely supported theory suggests yawning cools the brain by increasing blood flow and drawing cooler air into the sinus passages.
Studies show people yawn more frequently in warmer rooms, and cooling the forehead reduces yawning frequency significantly.
Another idea links yawning to alertness: it may help shift the brain from drowsy to awake states during transitions like waking up or boredom.
Contagious yawning — when seeing others yawn triggers your own — appears linked to empathy and develops around age four in children.
People with autism spectrum conditions or higher psychopathy scores tend to yawn less contagiously, supporting the empathy connection.
Even fetuses yawn in the womb, though they don’t breathe air — suggesting yawning plays a role in neural development.
Unlike sneezing or coughing, yawning isn’t triggered by irritation; it’s deeply tied to our circadian rhythms and social cues.