The Sun Makes Me Sneeze but Why?

Ever since I can remember I've been "allergic to the sun", or at least that's what I tell people when I go outside on a bright sunny day and suddenly sneeze on command. Actually, it doesn't even have to be a bright sunny day. I just go outside during daylight hours and I let two giant sneezes fly...and that's it, no more, no less.

I always figured I wasn't alone in my "allergy to the sun", since my father suffers from the same thing, but I had no idea how many people are affected by this until I started researching it. The statistics were a bit shocking.

It's called Photic Sneeze Reflex and it occurs in 17% to 25% of humans, with more common occurrences in Caucasians than other human races. Having an official name is fine and all (now I'm part of the P.S.R. club), but what exactly causes a person to be so sensitive to light that they sneeze?

The condition is passed along genetically as an autosomal dominant trait. And apparently it's a big problem for fighter pilots. Constant exposure to direct sunlight, above the clouds, can cause a pilot to have a sneezing attack at the worst possible time (incoming missile?). Since the early 1960's young hopefuls have been constantly rejected when they were found to have Photic Sneeze Reflex. ("The photic sneeze reflex as a risk factor to combat pilots," Military Medicine, Breitenbach et al, 1993.)

Scientifically speaking, over stimulation of the optic nerve in some people trigger the trigeminal nerve (the fifth cranial nerve), which is responsible for sneezing in humans. Additionally, Photic Sneeze Reflex can be brought on by sudden inhalation of cold air or a strong flavor in food such as mint or onion. This implies than almost any nerve close to the trigminal nerve can cause the Photic Sneeze Reflex to occur.

In layman's terms, you have a bunch of nerves crammed in the front of your head and bright lights can cause a mix up of signals. However, it's not really a problem, so don't stress out over it. Sunglasses can help out, but it's probably a good idea to stay out of that fighter jet.