Do you sneeze when you walk out of a dark tunnel into bright sunlight? You are not alone. This is called the photic sneeze reflex. About one in four people may have it. It can run in families.

Scientists found that, in these people, the part of the brain that sees is very sensitive to light. If you have it, you could try sunglasses.

Some people sneeze when they suddenly see bright light, for example when they leave a dark tunnel. This is a real condition called the photic sneeze reflex, and it is thought to affect about 18 to 35 percent of people. A 1993 report said it is passed from parents to children.

In 2010, a genetic study found gene variants near two genes that seem to be linked to it. In the same year, Swiss researchers measured brain waves and found that the visual area of the brain reacts more strongly to light in photic sneezers. The reflex may even be dangerous for fighter pilots who suddenly fly out of clouds into bright sky.

Sneezing in response to bright light may sound like a quirk of imagination, but the photic sneeze reflex is a well-documented phenomenon. A 1993 report in a military medical journal described it as an inherited trait present in roughly 18 to 35 percent of the population. Genetic evidence emerged in 2010, when the company 23andMe analyzed questionnaire answers from its customers alongside their genetic data and identified variants near the genes ZEB2 and NR2F2 associated with the reflex. However, this only points to candidate regions; no one knows how these genes might trigger sneezing, and many of the authors worked for the company.

Also in 2010, researchers at the University of Zurich recorded brain waves while showing participants patterns and flashing lights. Photic sneezers showed greater excitability in the visual cortex, and trials with stronger nasal tingling showed more activity in regions that process bodily sensation. The team proposed that the reflex involves specific areas of the cerebral cortex, not just a simple reflex deep in the brain, although the study was small. The reflex may even endanger fighter pilots who emerge suddenly into bright sky.