New York Times: Achoo! What’s That About?

The protective reflex of sneezing when exposed to bright light has not been heavily researched, even though it affects an estimated 18 percent to 35 percent of the population. That is because most people do not find it to be a serious problem, with many ignoring it, assuming that everyone reacts the same way they do.

The syndrome is known to be genetic, scientists reported in 1964.

Among the most recent research on the syndrome was a Spanish study this year published in The Archives of the Spanish Society of Ophthalmology, which found that 67 percent of the sufferers who were examined had prominent corneal nerves to some degree, an anomaly that could play a role in the reaction. The study was very small, however, involving 12 members of one family, and further research is needed, the authors said.

A 2005 study of electroencephalograms of brain activity, in the journal PLOS One, suggested that the reflex is unusual in involving specific higher brain areas governing vision and sensation, rather than a classical reflex that happens at the level of the brainstem or spinal cord.

One group for whom photic sneezing is not benign is fighter pilots, a 1993 study found. The reflex does not seem to be a reaction to specific wavelengths of light, but to changes in light intensity, which could set off an unexpected sneezing fit during critical periods of flight, the researchers said.