Why do some people sneeze when going out into bright light?
Ever since I was a tiny infant, I have sneezed when going out into the bright sun. My momma confirms this fact, but can't give me a more satisfactory cause than the empirical statement that I've always done it. Three decades later, I still produce the obligatory two or three sneezes seconds after walking into bright sunlight. (It doesn't happen on a cloudy day or at night.) I remember several years ago reading in the paper that some percentage of people experienced sun-induced sneezing fits, but they didn't say why. What's the deal?
You are thinking this is a matter of idle curiosity, Alan? Au contraire — it's a threat to our national security. Listen to this frightening headline: "The photic sneeze reflex as a risk factor to combat pilots," Military Medicine, Breitenbach et al, 1993. "Photic sneeze reflex" is the medical term for what you've got. Researchers fear they'll get a guy like you in a screaming dogfight, you break through the clouds into bright sunlight, you sneeze, your eyes snap shut, and the next thing you know they're picking you up off the landscape with a rake. Photic sneeze reflex occurs in something like one-sixth to one-quarter of the population. It occurs more often in Caucasians than Afro-Americans or Orientals. According to a Johns Hopkins medic named Stephen Peroutka, the trait is passed along genetically, with a 50 percent chance of inheritance. Researchers in Sweden found that out of 460 subjects, 24 percent sneezed in bright light, and 40 percent had at least one sneezing parent. Sixty-four percent of children with one sneezing parent were themselves sneezers, but two nonsneezers never produced a sneezer. (Isn't it amazing how I can make these things so easy to understand?)
Nobody's exactly sure what causes photic sneeze reflex. I see here in one of the journals we have an impressive discussion of the role of the trigeminal nerve nucleus. Basically what this is saying is that you've got a lot of nerves crammed together in the front of your head, and maybe there can can be leakage of sorts from one nerve pathway to another. So perhaps the reflex is just a case of congenitally crossed signals. At this point nobody's prepared to go in there with a pliers and fix it. So your best bet is to wear sunglasses and stay out of fighter jets.
From the Teeming Millions
Re "photic sneeze reflex": When we cry, we need to blow our noses. Therefore, there is a passage from the tear ducts to the nose. Photic sneeze reflex is caused by tears (our eyes water to protect the unadjusted irises from bright lights) moving into the nasal passages, tickling the hairs within. The result: kerchoo!
As a matter of fact, there IS a passage connecting the tear ducts to the nose called the nasolacrimal duct. It enables tears to drain out of the eye.
Some researchers agree that tears leaking into the nose are a possible cause of photic sneeze reflex.
However, an ear-nose-and-throat specialist I spoke to, who experiences PSR, says sneezing occurs immediately upon emerging into the light, too quickly for tears to work their way down the duct.
Once I get all the world's other problems squared away, such as what Steve Miller was talking about when he sang "I speak of the pompatus of love," I'll get to the bottom of PSR. (The Straight Dope: What is the "pompatus of love?" October 25, 1996) But for right now all I can say is I dunno.