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From: york@mbcrr.dfci.harvard.edu (Ian A. York)
Newsgroups: alt.folklore.urban
Subject: Allergic to sunlight?
Date: 14 Aug 1995 17:47:37 GMT

Apparently one of the fringe benefits of having a Nobel Prize (besides the free bowling shoe rental in Sweden) is that all kinds of science journals send you their issues free. The Nobel Laureate whose office is three doors down from me drops these off in our lunch room, and I have one of them sitting right here on my lap: The Guthrie Journal is a peer-reviewed quarterly medical journal, which has a nifty little review of the photic sneeze reflex.

Sneezing response to bright light. Is it a cause of accidents? N. Deshmukh
The Guthrie Journal, 64(3):104-105 (1995)

Exerpted - typos are mine.

"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 accident. ... It is also possible that this could be the cause of automobile accidents. During a sneeze, there is an involuntary closing of the eyes momentarily. ...

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

When the subjects were interviewed, 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.

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. During the interviews, I found that some of the subjects could 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 ofthe nasal cavity and a sneeze.

Breitenbach and others studied the effects of various light wave lengths to see which, if any, would be more likely to cause a sneeze. They found no diffrence. They also found that the response could be prevented by wearing sunglasses. ...
...

Until there are more data, this should not be cause for grounding any pilot. Drivers of automobiles should also be aware of possible momentary loss of control when exposed to sudden bright light."

Ian "I just crumble into dust when exposed to bright light" York