Welcome to brain Stuff from how Stuff Works. Hey, brain stuff. Lauren vog obam here with today's question, why do some people sneeze when suddenly exposed to bright light like sunlight? Only about ten to 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 ophthalmic outbursts of sneezing. And don't worry, we'll get back to some of those terms in a minute. People have 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. Unfortunately, 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 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're one of the seventy to nine 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 photox sneezing gene. If one of them has it, you have a fifty percent chance of being a photo sneezer yourself. But the question of why remains. No absolutely conclusive answer has been reached, But there's one very interesting theory.
Photox sneezing happens because some wires are crossed in your head. Normally, a sneeze is your noses 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 photo sneezer are suddenly exposed to bright sunlight. The optic nerve detects this and sends another reflix signal too bright drink by 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 was
written by Joe McCormick and produced by Tyler Clang. For more on this and lots of other topics about our weird bodies, visit our home planet, how Stuff Works dot com.