What Happens in Your Body When You Sneeze?


It happens all the time — when the air is dusty, when allergies strike, when you catch a cold or the flu. In one forceful blow, your body manages to send your torso heaving and spew snot in all directions at seriously impressive speeds. And you’re powerless to stop it. But what is a sneeze? There are some wacky things that happen in your body with every “achoo!”

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There are hundreds of tiny little hairs lining your nasal cavity that are attached to receptors. When these receptors are irritated by a foreign object (such as dust or mold) trapped in these hairs, they send a signal to your brain that it’s time to clear things out. These receptors are very sensitive and are bothered by even the tiniest of particles. Mucus tends to trap particles, which is why you sneeze so often when you’re sick.

Around 10 to 35 percent of people can also sneeze because they’re exposed to bright light, according to a study found in the Archives of the Spanish Society of Ophthalmology. It’s a condition called Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome (which, ironically, scientists refer to by the acronym ACHOO). Researchers have theories, but they still haven’t really figured out why light triggers the same reflex in the brain.

Once your brain receives the sneeze signals, it’s go time. A sneeze is no joke — air flies out of your nose at crazy high speeds. Mythbusters found it was around 30 to 40 miles per hour. To brace for impact, your body triggers a reflex that tenses the muscles in your nose, moves your tongue to the roof of your mouth, squeezes your eyes shut and freezes you to the spot.

You breathe in sharply. After your lungs fill with air, your throat closes so as not to allow any to escape. Then, in one quick contraction, your chest muscles squeeze all the air from your lungs. The bigger your breath (and the larger your lung capacity), the more aggressive your sneeze.

This gust of wind forces mucus, dust and germs out of your nose and mouth. Thousands of droplets spray from your face. If the blow wasn’t effective enough in getting rid of the gunk, you’ll likely sneeze again.

While sneezing actually won’t stop your heart (that’s one of many health myths you can stop believing), for some people, the whoosh of air that enters and exits the lungs disrupts the heart’s normal rhythm. The deep inhale that happens right before a sneeze builds enough pressure in your chest to slow blood flow to your heart. Breathing in also increases the heart’s BPM (beats per minute) in order to disperse inhaled oxygen. When you quickly breathe out, the pressure around your heart drops, suddenly increasing blood flow. BPM also drops when you exhale. This quick fluctuation may affect your heartbeat for a second or two, but don’t worry. The effect is almost always benign.

So there you have it — the biology of a sneeze, from start to finish. Next allergy season, you can be well prepared for this and all the other weird ways seasons affect your body.