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Everyone does it, but why? In this episode of SciShow Quick Questions you get the answers!

Hosted by: Michael Aranda
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Michael: Everyone, everywhere occasionally sneezes. It’s something humans—and even some animals like cats, and dogs, and chickens —just do. But why? Why do we sneeze? If your answer is that it’s our nose’s way of getting rid of irritants and excess mucus, you’re right -- but only partly.

See, scientists have long thought that sneezing -- technically known as sternutation -- is a reflex. When irritants -- like dust, dander, germs, or pollen -- get into your nose, your brain sends out a signal to get rid of it. That same signal goes out if an excessive amount of mucus is hanging out in there too -- say, if you have a cold. This signal triggers a deep breath, which you hold in your lungs for a moment. While you’re holding your breath, your chest muscles clench and pressure builds. Your tongue is forced to the roof of your mouth... and you breathe out -- fast -- through your nose in the form of a sneeze. That’s the old, short, and still correct answer to the question “Why do we sneeze?”

But according to a paper published in 2012 in the journal FASEB, there’s a little more to it than that. And it all has to do with cilia, the tiny, hairlike paddles that line our noses and sinuses. In the study, a group of researchers from the University of Pennsylvania basically grew a tiny nose. They took cells from the nostrils of several healthy adults and grew them in an incubator for a few weeks, until the cells formed the same type of lining that's in your sinus, complete with cilia.

Then, to mimic a sneeze, the scientists puffed air on the lining. They noticed that the burst of air triggered the cilia—which look sort of like shaggy dog hair under a microscope—to kick into high gear, moving back and forth repeatedly for up to several minutes after the trick sneeze. So, why were they so active for so long? Any potential irritants would have been cleared out already. Well, the triggered cilia were acting as a broom, basically resetting the entire nasal environment, not just the parts where there’d been irritating gunk.

Just like computers do, biologists think that our nose needs a reboot every once in a while... and its kinda-furry restart button is made of all those cilia. But it turns out that not everybody’s sneezes actually reboot their nose. In addition to looking at healthy folks’ cells, this same group of scientists took a peek at the cells of people suffering from sinusitis, which causes inflamed sinuses and general nasal discomfort—runny nose, nasal congestion, all that fun stuff. They discovered that when they puffed air onto the tissue of the sinusitis sufferers, the cilia didn’t beat faster. Meaning that chronic sinusitis might have to do with cilia that can’t properly reset post-sneeze -- and that knowledge might help researchers developing treatments for it.

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