Photic Sneeze Reflex (AKA Sun Sneezing)

Many of us, including myself, have experienced the sudden need to sneeze after walking outside into bright sunlight. This phenomenon is called the Photic Sneeze Reflex, and it is reported to affect 10%-35% of the population. There is no known explanation for the phenomenon, but scientists have traced the genes which are responsible for passing on this trait. One hypothesis, proposed by Henry Everett in 1964, claims that this phenomenon is caused by two nerve pathways which are a little too close to each other. According to the hypothesis, the bright light causes a great number of nerve signals to travel down the optic nerve, which stimulates the nearby trigeminal nerve that is involved in the sneeze reflex. The result is the need to sneeze. Though this hypothesis sounds pretty good, it lacks any supporting evidence. Another hypothesis proposes that the cause is a mixup of signals in the part of the brainstem responsible for these reflexes. Some scientists have tried to explain the photic sneeze reflex through evolution, saying that this reflex was useful to cavemen who needed to clear dust out of their noses after emerging from their dirty caves. While the cause of this phenomenon remains unknown, we who suffer from this reflex can rest assured that there are no negative consequences of sun sneezing.