Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff, Lauren Vogelbomb here with a classic episode of the podcast. Today's delves into the weird nerve wiring in our faces that can make people sneeze even when nothing's bothering your nose at all. Rather, you've just seen a bright light. Hey brain Stuff, Lauren vogel Bomb here with today's question, why do some people sneeze when suddenly exposed to bright light like sunlight? Only about ten to thirty five percent
of people do this. I happen to be one of them. And no, we're not allergic to the sun. We may be the proud owner of a photic sneeze reflex or PSR, also known as at Chew syndrome. And yes that's an acronym.
It stands for autosomal dominant compulsive helio ophthalamic outbursts of sneezing. And don't worry, we'll get back to some of those terms in a minute. Been trying to figure out the cause of the photic sneeze for thousands of years. The ancient Greek philosopher Aristotle or an unknown author writing in his name, asked, why does the heat of the sun provoke sneezing and not the heat of the fire. Good question,
Aristotle or fake. Aristotle's answer to himself was because the heat of the sun doth dissolve but not consume, and therefore the vapor dissolved is expelled by sneezing. So his theory is that the heat of the sun makes the inside of your nose wet, and you've got to purge that liquid with a good sneeze. M Fortunately, in the seventeenth century, the English science pioneer Francis Bacon decided to put Aristotle to the test.
He showed that if a photic.
Sneezer walks into the sun with his or her eyes closed, the reflex is not triggered. Therefore we know it's not caused by the heat. It's caused by your eyes reacting to light. So what do we know about the photic sneeze today. Well, one study in nineteen ninety three found that it's not any particular wavelength of light that causes the problem, So you can't protect against it by just
filtering out red light or violet light or anything in between. Instead, it has to do with the intensity of the light. So the good news is that if you want to avoid the photic sneeze, there's a pretty easy solution that works most of the time. Plain old sunglasses.
Also more good news.
If you are one of these seventy to ninety percent of people listening and thinking, what on earth is she talking about? Am I going to catch this sneeze disease someday? You can rest easy. You can't acquire the photic sneeze reflex after birth. It's a genetic trait. A study in the nineteen sixties found that this trait is inherited through an autosomal dominant mechanism. This means that it doesn't matter
which of your parents has the photic sneezing gene. If one of them has it, you have a fifty percent chance of being a photic sneezer yourself. But the question of why remains. No absolutely conclusive answer has been reached. But there's one very interesting theory. Photic sneezing happens because some wires are crossed your head. Normally, a sneeze is your nose's version of the passenger eject seat in James Bond's car. Sneezing begins when irritation in the nose is
detected by an organ called the trigeminal nerve. When that nerve senses an unpleasant foreign substance, it sends the eject signal to the brain. But inside your head, this nerve runs very close to the optic nerve, which senses light in the eyes. So let's say the eyes of a photic sneezer are suddenly exposed to bright sunlight. The optic nerve detects this and sends another reflex signal ah to
bright trink my pupils. But if the optic nerve runs a little too close to the trigeminal nerve, the pupil constriction signal also gets interpreted as a something's in my nose signal and Bam sneezing fit. Today's episode is based on a videoscript for houstuffworks dot Com written by Joe McCormick. Brain Stuff is production of iHeartRadio in partnership with how
Stuffworks dot Com. It is produced by Tyler Klang. Four more podcasts from my Heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.