WEBVTT - BrainStuff Classics: How Can Sunlight Make You Sneeze?

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<v Speaker 1>Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff,

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<v Speaker 1>Lauren Vogelbomb here with a classic episode of the podcast.

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<v Speaker 1>Today's delves into the weird nerve wiring in our faces

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<v Speaker 1>that can make people sneeze even when nothing's bothering your

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<v Speaker 1>nose at all. Rather, you've just seen a bright light.

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<v Speaker 1>Hey brain Stuff, Lauren vogel Bomb here with today's question,

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<v Speaker 1>why do some people sneeze when suddenly exposed to bright

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<v Speaker 1>light like sunlight? Only about ten to thirty five percent

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<v Speaker 1>of people do this. I happen to be one of them.

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<v Speaker 1>And no, we're not allergic to the sun. We may

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<v Speaker 1>be the proud owner of a photic sneeze reflex or PSR,

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<v Speaker 1>also known as at Chew syndrome. And yes that's an acronym.

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<v Speaker 2>It stands for autosomal dominant compulsive helio ophthalamic outbursts of sneezing.

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<v Speaker 2>And don't worry, we'll get back to some of those

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<v Speaker 2>terms in a minute. Been trying to figure out the

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<v Speaker 2>cause of the photic sneeze for thousands of years. The

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<v Speaker 2>ancient Greek philosopher Aristotle or an unknown author writing in

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<v Speaker 2>his name, asked, why does the heat of the sun

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<v Speaker 2>provoke sneezing and not the heat of the fire. Good question,

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<v Speaker 2>Aristotle or fake. Aristotle's answer to himself was because the

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<v Speaker 2>heat of the sun doth dissolve but not consume, and

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<v Speaker 2>therefore the vapor dissolved is expelled by sneezing. So his

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<v Speaker 2>theory is that the heat of the sun makes the

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<v Speaker 2>inside of your nose wet, and you've got to purge

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<v Speaker 2>that liquid with a good sneeze. M Fortunately, in the

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<v Speaker 2>seventeenth century, the English science pioneer Francis Bacon decided to

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<v Speaker 2>put Aristotle to the test.

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<v Speaker 1>He showed that if a photic.

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<v Speaker 2>Sneezer walks into the sun with his or her eyes closed,

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<v Speaker 2>the reflex is not triggered. Therefore we know it's not

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<v Speaker 2>caused by the heat. It's caused by your eyes reacting

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<v Speaker 2>to light. So what do we know about the photic

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<v Speaker 2>sneeze today. Well, one study in nineteen ninety three found

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<v Speaker 2>that it's not any particular wavelength of light that causes

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<v Speaker 2>the problem, So you can't protect against it by just

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<v Speaker 2>filtering out red light or violet light or anything in between. Instead,

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<v Speaker 2>it has to do with the intensity of the light.

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<v Speaker 2>So the good news is that if you want to

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<v Speaker 2>avoid the photic sneeze, there's a pretty easy solution that

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<v Speaker 2>works most of the time. Plain old sunglasses.

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<v Speaker 1>Also more good news.

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<v Speaker 2>If you are one of these seventy to ninety percent

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<v Speaker 2>of people listening and thinking, what on earth is she

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<v Speaker 2>talking about? Am I going to catch this sneeze disease someday?

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<v Speaker 2>You can rest easy. You can't acquire the photic sneeze

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<v Speaker 2>reflex after birth. It's a genetic trait. A study in

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<v Speaker 2>the nineteen sixties found that this trait is inherited through

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<v Speaker 2>an autosomal dominant mechanism. This means that it doesn't matter

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<v Speaker 2>which of your parents has the photic sneezing gene. If

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<v Speaker 2>one of them has it, you have a fifty percent

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<v Speaker 2>chance of being a photic sneezer yourself. But the question

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<v Speaker 2>of why remains. No absolutely conclusive answer has been reached.

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<v Speaker 2>But there's one very interesting theory. Photic sneezing happens because

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<v Speaker 2>some wires are crossed your head. Normally, a sneeze is

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<v Speaker 2>your nose's version of the passenger eject seat in James

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<v Speaker 2>Bond's car. Sneezing begins when irritation in the nose is

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<v Speaker 2>detected by an organ called the trigeminal nerve. When that

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<v Speaker 2>nerve senses an unpleasant foreign substance, it sends the eject

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<v Speaker 2>signal to the brain. But inside your head, this nerve

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<v Speaker 2>runs very close to the optic nerve, which senses light

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<v Speaker 2>in the eyes. So let's say the eyes of a

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<v Speaker 2>photic sneezer are suddenly exposed to bright sunlight. The optic

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<v Speaker 2>nerve detects this and sends another reflex signal ah to

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<v Speaker 2>bright trink my pupils. But if the optic nerve runs

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<v Speaker 2>a little too close to the trigeminal nerve, the pupil

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<v Speaker 2>constriction signal also gets interpreted as a something's in my

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<v Speaker 2>nose signal and Bam sneezing fit. Today's episode is based

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<v Speaker 2>on a videoscript for houstuffworks dot Com written by Joe McCormick.

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<v Speaker 2>Brain Stuff is production of iHeartRadio in partnership with how

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<v Speaker 2>Stuffworks dot Com. It is produced by Tyler Klang. Four

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