The photic sneeze reflex causes about 10% of the population to sneeze when exposed to sudden bright light. Here's a Youtube video from the Great Big Story channel that gives a nice overview:
The exact mechanism that underlies the protonic sneeze reflex is still unknown! Here is a 20k RSC bounty for any ResearchHub user who can create a concise, but up-to-date narrative review with properly cited sources that explores a potential hypothesis to explain the mechanism of action behind this reflex.