十万个为什么·科学启蒙30篇（3）

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鼻子发出紧急信号，你就打喷嚏

When dust, pollen, or cold air tickles your nasal passages, nerves send a fast alert.
Your brain tells your lungs to take a deep breath and push air out hard.
Muscles in your chest, throat, and face all squeeze together in one quick motion.
That rush of air shoots out at over 100 miles per hour to clear irritants.
Your eyes close automatically during the sneeze to protect them from germs.
Covering your mouth with your elbow helps stop tiny droplets from flying far.
Some people sneeze when they walk into bright sunlight — scientists call this the photic reflex.
Sneezing too often might mean allergies or a cold is starting.
It’s polite to say 'Excuse me' right after you sneeze in public places.
Doctors suggest washing hands often because sneezes spread germs easily.