Roberta A. Pagon, a professor of pediatrics at the University of Washington, explains.

Reflexive sneezing induced by light, and sunlight in particular, is estimated to occur in 18 to 35 percent of the population and is known as the photic sneeze reflex (PSR) or the ACHOO (autosomal dominant compulsive helio-ophthalmic outbursts of sneezing) syndrome. Its genetic nature has been known for at least the last 25 years; it is periodically discussed in the medical literature and lay press. Observations that emerging from dim light into sunlight or turning to face directly into the sun commonly triggers the reflex prompted early inquiries into the trait. The number of induced sneezes--which seems to be genetically mediated and can be predicted within a family--is constant from episode to episode and typically numbers two or three.

Some consequences of the PSR include danger to automobile drivers when emerging from dim light, such as a tunnel, into full sunlight, and disruption of outdoor group photos. More recently, reports in publications oriented to military medicine have noted the potential danger to pilots experiencing the PSR. In fact, studies conducted by the military revealed that the PSR is not mediated by specific wavelengths of light and thus cannot be mitigated by the use of filtering lenses; rather the investigators concluded that the PSR is induced by changes in light intensity. Others have not found flickering light to precipitate the PSR. Exactly how sunlight causes some people to sneeze remains unknown.

4 Comments

1. 1. steve mossman 02:12 PM 1/12/08

   Look at and compair Head Shaking in horses, info at U C Davis

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2. 2. egghead1619 12:24 PM 8/26/09

   I was just talking about this to my wife after I noticed our newborn sneezing when some sunshine hit his face. I've always used the sun to invoke a sneeze when I have one on the verge and just burning. I've never really noticed it with anything other than the sun for me. Perhaps he received the PSR from me and the multiple sneezes (at least 3 in short order) from my wife; poor kid.

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3. 3. KeithPearson 09:43 AM 12/10/12

   Completely out of the blue, my son asked me why looking at bright light helps him to sneeze when he feels one coming-on. I hasn't realised it was was genetic.

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4. 4. DannyS 10:44 AM 1/20/13

   It seems to me that, in order to understand this phenomenon, the question that should be asked is: under what circumstances would our ancestors have encountered a sudden transition from darkness to bright light? The answer is, when exiting from a cave into the open air. Since the air in a cave is likely to be filled with various kinds of particulate matter, it would make sense to clear the nasal passages of such matter when leaving the cave behind, and a sneeze is an excellent way to do that.

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