BBC - h2g2 - Photic Sneezing

I suffer from a bizarre, but often highly amusing trait called photic sneeze reflex. If I step outside into bright sunlight, look directly into the sun, or even walk into a very bright room, I will sneeze loudly, and often, to quite catastrophic effect. I have suffered numerous minor injuries due to falling over, headbutting inanimate objects - walls, doors, steering wheels. It is in the car that this trait has the greatest capacity to terrify. Passangers of mine have reacted with horror, as I have sneezed violently (cracking my head on the steering wheel) while travelling at considerable speed in the outside lane of a motorway.

"About 20% of people sneeze because of reflex action when exposed to sudden, bright light. If this happens at a critical phase of flying a rotary or fixed wing aircraft, it could result in loss of control of the aircraft and a serious accident¹. It is also possible that this could be the cause of some automobile accidents, since, during a sneeze, there is, momentarily, an involuntary closing of the eyes.

The typical sneezing response occurs when the individual comes out of a dark surrounding into sudden bright light such as when leaving a cinema. Within a period of two to fifteen seconds, the individual may sneeze one or more times.

When people have been interviewed about photic sneezing, those who had this reflex assumed that everyone had it, and those who did not have it were puzzled as to why such a question should be asked. Many of my friends refused to believe it until they witnessed it first hand. It was at this point that I found that I had a fair level of control over voluntary inducement of photic sneezing!

Various studies have shown a strong autosomal dominant inheritance. The problem seems to occur more often in Caucasians, but it has also been found to occur in Afro-Americans as well as Orientals. There appears to be no predominance in either sex. In studies it has been found that some of individuals can control the reflex, at least some of the time, especially when they expected it to occur.

Mechanism of the Photic Sneeze

The mechanism of the bright light sneeze reflex seems to be an association of optic nerve fibers and trigeminal nerve nucleus in the mid-brain. The trigeminal nerve's second division supplies sensory fibers to the nasal mucosa. It is postulated that nerve impulses travelling up the optic nerve will cause a sympathetic discharge down the trigeminal nerve fibers. Another mechanism postulates that partial squinting of the eyes resulting from the bright light causes squeezing of the lacrimal sac which results in tears running down the nasolacrimal duct into the nasal cavity, causing stimulation of the nasal cavity and a sneeze.

Breitenbach et al. studied the effects of various light wave lengths to see which, if any, would be more likely to cause a sneeze. They found no difference. They also found that the response could be prevented by wearing sunglasses. (Well duh!)

Fortunately, there is no chance of your eyeballs falling out during photic sneezing.

¹ Airline pilots are not tested for their susceptibility to the photic sneeze reflex, so if you are on a flight, and there is a sudden flurry of turbulence after going through cloud you'll know why (just pray the sun doesn't come out half way through take-off!).