Simply put, it’s sneezing when exposed to bright sunlight. It’s estimated that 18-35% of the population has this disorder. I say disorder only in the sense of it being irritating, but there is no serious problem with it unless you’re driving a vehicle and suddenly are wracked with sneezing.
I find that if I go from inside a car or house into bright sunlight without dark glasses and a hat, I will sneeze about three times. As mentioned above, I never had this when younger so don’t know why it started up as I approached geezerhood.
I’ve used this syndrome in one novel I’ve written.
Do you ever sneeze when exposed to bright sunlight?