十万个为什么·科学启蒙30篇（2）
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Why Do We Yawn?
我们为什么会打哈欠？
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Yawning is a reflex involving deep inhalation, stretching of jaw muscles, and often a slow exhalation — but its exact purpose remains debated.
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One widely supported theory suggests yawning cools the brain by increasing blood flow and drawing cooler air into the sinus passages.
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Studies show people yawn more frequently in warmer rooms, and cooling the forehead reduces yawning frequency significantly.
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Another idea links yawning to alertness: it may help shift the brain from drowsy to awake states during transitions like waking up or boredom.
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Contagious yawning — when seeing others yawn triggers your own — appears linked to empathy and develops around age four in children.
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People with autism spectrum conditions or higher psychopathy scores tend to yawn less contagiously, supporting the empathy connection.
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Even fetuses yawn in the womb, though they don’t breathe air — suggesting yawning plays a role in neural development.
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Unlike sneezing or coughing, yawning isn’t triggered by irritation; it’s deeply tied to our circadian rhythms and social cues.