Ever wonder why sudden exposure to sunlight makes you sneeze?
It turns out that that process has a name. It’s called photic sneeze reflex, or ACHOO. ACHOO stands for Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome. It occurs in about 25% of people and is genetic.
While this syndrome has been known for years, no one knows exactly why people suffer from it. However, some scientists have a really interesting theory.
First, people already know what triggers the sneeze. No particular wavelength of light causes the sneeze reaction, but rather it has to do with the intensity of the light you look at. Second, photic sneeze reflex is known to be a genetic condition. Clearly, it must be a defect in one area of the nerves, or so the following theory goes.
Some scientists believe photic sneeze reflex is caused by a glitch in one of the brain’s main nerves, the trigeminal nerve. Before you sneeze, the trigeminal nerve is what detects irritation in your nose. But the trigeminal nerve runs close to your optic nerve, which senses light in the eyes. So if someone is suddenly exposed to direct sunlight, the optic nerve senses this. But because it’s so close to the trigeminal nerve, the light is also detected as an irritation in the nose, which causes you to sneeze.
Essentially, in those of a certain genealogy, their trigeminal nerve and optic nerve overlap, causing the slight irritation when people are exposed to the bright light.
This isn’t the only theory for the cause of photic sneeze reflex, but it is the most convincing.
Sadly, it seems like this condition is wholly incurable. Those who do have photic sneeze reflex will be stuck with it for life and possibly pass it on to their children.
Next time you sneeze from this syndrome, or witness a friend who suffers from it, at least there will be some satisfaction in knowing what probably causes it.