The explanation why some people tend to sneeze when exposed to bright light remains an enigma. There are indications that certain variants may increase the predisposition to this particular trait.
Photic sneeze reflex
The "photic sneeze reflex" is a characteristic of some people who tend to sneeze when they move from relative darkness to bright light, often sunlight (e.g., when exiting a tunnel). Once the eyes have adapted to the brightness the sneezing stops. This condition occurs in about one in four Caucasians and is thought to have a hereditary component.
The exact cause of this reflex and whether it has any physiological relevance is unknown, but it is thought to be due to an electrical process in which light stimulates several nerves involved in the sneeze reflex.
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Eriksson N, Macpherson JM, Tung JY, Hon LS, Naughton B, Saxonov S, et al. Web-based, participant-driven studies yield novel genetic associations for common traits. PLoS Genet. 2010;6(6):1–20.
Wang M, Sun X, Shi Y, Song X, Mi H. A genome-wide association study on photic sneeze reflex in the Chinese population. Sci Rep. 2019 Mar 21;9(1):4993.