Speaker 1: Welcome to brain Stuff from how Stuff Works. Hey, brain stuff.
Speaker 1: Lauren vog obam here with today's question, why do some
Speaker 1: people sneeze when suddenly exposed to bright light like sunlight?
Speaker 1: Only about ten to of people do this. I happen
Speaker 1: to be one of them, And no, we're not allergic
Speaker 1: to the sun. We may be the proud owner of
Speaker 1: a photic sneeze reflex or PSR, also known as at
Speaker 1: Chew syndrome. And yes, that's an acronym. It stands for
Speaker 1: autosomal dominant compulsive helio ophthalmic outbursts of sneezing. And don't worry,
Speaker 1: we'll get back to some of those terms in a minute.
Speaker 1: People have been trying to figure out the cause of
Speaker 1: the photic sneeze for thousands of years. The ancient Greek
Speaker 1: philosopher Aristotle or an unknown author writing in his name, asked,
Speaker 1: why does the heat of the sun provoke sneezing and
Speaker 1: not the heat of the fire? Good question, Aristotle or
Speaker 1: fake Aristotle's answer to himself was because the heat of
Speaker 1: the sun doth dissolve but not consume, and therefore the
Speaker 1: vapor dissolved is expelled by sneezing, So His theory is
Speaker 1: that the heat of the sun makes the inside of
Speaker 1: your nose wet, and you've got to purge that liquid
Speaker 1: with a good sneeze. Unfortunately, in the seventeenth century, the
Speaker 1: English science pioneer Francis Bacon decided to put Aristotle to
Speaker 1: the test. He showed that if a photic sneezer walks
Speaker 1: into the sun with his or her eyes closed, the
Speaker 1: reflex is not triggered. Therefore, we know it's not caused
Speaker 1: by the heat. It's caused by your eyes reacting to light.
Speaker 1: So what do we know about the photic sneeze today, Well,
Speaker 1: one study in found that it's not any particular wavelength
Speaker 1: of light that causes the problem, So you can't protect
Speaker 1: against it by just filtering out red light or violet
Speaker 1: light or anything in between. Instead, it has to do
Speaker 1: with the intensity of the light. So the good news
Speaker 1: is that if you want to avoid the photic sneeze,
Speaker 1: there's a pretty easy solution that works most of the time,
Speaker 1: plain old sunglasses. Also more good news. If you're one
Speaker 1: of the seventy to nine of people listening and thinking,
Speaker 1: what on earth is she talking about? Am I going
Speaker 1: to catch this sneeze? Disease. Someday you can rest easy.
Speaker 1: You can't acquire the photic sneeze reflex after birth. It's
Speaker 1: a genetic trait. A study in the nineteen sixties found
Speaker 1: that this trait is inherited through an autosomal dominant mechanism.
Speaker 1: This means that it doesn't matter which of your parents
Speaker 1: has the photox sneezing gene. If one of them has it,
Speaker 1: you have a fifty percent chance of being a photo
Speaker 1: sneezer yourself. But the question of why remains. No absolutely
Speaker 1: conclusive answer has been reached, But there's one very interesting theory.
Speaker 1: Photox sneezing happens because some wires are crossed in your head. Normally,
Speaker 1: a sneeze is your noses version of the passenger eject
Speaker 1: seat in James Bond's car. Sneezing begins when irritation in
Speaker 1: the nose is detected by an organ called the trigeminal nerve.
Speaker 1: When that nerve senses an unpleasant foreign substance, it sends
Speaker 1: the eject signal to the brain. But inside your head,
Speaker 1: this nerve runs very close to the optic nerve, which
Speaker 1: senses light in the eyes. So let's say the eyes
Speaker 1: of a photo sneezer are suddenly exposed to bright sunlight.
Speaker 1: The optic nerve detects this and sends another reflix signal
Speaker 1: too bright drink by pupils. But if the optic nerve
Speaker 1: runs a little too close to the trigeminal nerve, the
Speaker 1: pupil constriction signal also gets interpreted as a something's in
Speaker 1: my nose signal and Bam sneezing fit. Today's episode was
Speaker 1: written by Joe McCormick and produced by Tyler Clang. For
Speaker 1: more on this and lots of other topics about our
Speaker 1: weird bodies, visit our home planet, how Stuff Works dot com.