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SciShow's Quick Questions explains why bright light can make some people sneeze! Really!
Hosted by: Michael Aranda
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About one third of the people on Earth will tell you that this is a thing.

The other two-thirds probably think that the first third is crazy, but they’re too polite to say anything.

But if you’ve ever walked out of dark matinee theater, or driven out of a long tunnel and into the sunlight, and then suddenly SNEEZED, you’re probably experiencing one of medical science’s least-understood-but-thankfully-harmless phenomena.

It’s known as photic sneezing -- or sneezing triggered by sudden exposure to bright light. And it happens to about 30 to 35 percent of us.

So take that all you nay-sayers! It’s real! But scientists don’t know why.

References to light-triggered sneezing show up in medical literature as far back as Aristotle. But modern researchers started looking into it more closely, when they realized that a poorly timed photic sneeze could pose a big problem for people like surgeons and airplane pilots.

So far, the best we can figure is that light-triggered sneezing has to do with an interaction between overactive sensory nerves.

A study in 2010, for instance, examined ten photic sneezers, as well as a control group. After exposing all of the subjects to bright, flashing light, the researchers found that the light triggered a lot more activity in the visual cortex of the photic sneezers’ brains than in the control group. So it could just be that sneezers’ sensitivity to light is just more excitable than in other people.

But the prevailing theory has to do with a specific, complex nerve bundle called the trigeminal nerve, which is the biggest nerve in your head.

It is responsible for all of the sensation in your entire face, from the tickle in your nose to the twitch in your eyebrows to that feeling of needing Chapstick.

And parts of this nerve also sidle up nice and close to your optic nerves, which transmit the information your brain gets about light entering your eyes.

So the theory is that a sudden flash of bright light stimulates the optic nerve, which sometimes also transmits an impulse to the nearby branches of the trigeminal nerve that connect to the nose and mouth.

This impulse mimics the tickle of a nasal irritation, which then causes you to sneeze.

So while we’re not exactly sure about how it works, this scenario might explain why other weird things can trigger sneezing that also involve stimulating the trigeminal nerve -- like pulling hair, or plucking eyebrows.

So if you’re a photic sneezer, there’s no need to hide it anymore. Be proud!

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