When the Sun makes you sneeze, it’s called a photic sneeze reflex, and it occurs in about a quarter of the population.
What happens to convince your nose that the sun is an object that must be sneezed out of your nasal cavities? It’s simply a case of crossed wires, like hearing interference on your phone line from someone else’s conversation.
There are so many nerves running through your facial and nasal cavities that some of them end up right next to one another. Stepping into bright light sends rapid signals through your optical nerves to your brain so that it can instruct your pupils to dilate and your lids to squint in response.
Some of these optic nerves butt up against the nasal nerves and trigger a wildly inappropriate responsea sneeze.
Do you cough or choke while cleaning your ears? A similar signal-crossing scenario may be taking place.