Why do some people sneeze when they step into bright sunlight?

Ever wonder why you sneeze when you step into the sun? You’ve got the Photic Sneeze Reflex, or ACHOO syndrome, which affects about 18 to 35% of the population^[1][2]. It’s a genetic, autosomal dominant trait, meaning if one parent has it, there’s a 50% chance you inherited it too^[2][5]. Scientists think it’s basically a neurological mix-up where a sudden change in light intensity triggers the trigeminal nerve, which the brain mistakes for a nasal irritant^[1][4][6].

It’s usually just a harmless quirk, but it can be annoying or even dangerous if you’re driving or flying and lose focus during a sneezing fit^[1][6]. Think of it like exiting a dark movie theater into bright daylight and suddenly needing to sneeze your head off^[2][4].