The photic sneeze reflex is a reflex condition that causes sneezing in response to numerous stimuli, such as looking at bright lights or periocular (surrounding the eyeball) injection. The condition affects 18–35% of the world's population"

Source :Wikipedia

Its cause, and the tendency for inheritance within families, are unknown.

There are a number of theories, but none has been generally accepted - see, for example : Photic sneeze reflex: another variant of the trigeminocardiac reflex? Future Neurology, Vol. 14, No. 4 Special Report

Note : It's also known as 'Autosomal Compelling Helio-Ophthalmic Outburst' (ACHOO) syndrome (Source :Medical Genetics Summaries)

Also see :Sneeze centerplugin-autotooltip__plain plugin-autotooltip_bigSneeze center

"Experiments in cats identified a concentration of cells in the rostral dorsolateral pontomedullary area, stimulation of which causes sneezing indistinguishable from sneezing induced by natural peripheral stimuli."

Source : Localization of the “sneeze center” Neurology Journal,