Part of the show Science Question and Answer - New Horizons Mission
Les in Peterborough asked:
How come I sneeze when I stare at the sun in the morning?
That is called the photic sneeze reflex and it's something that's a big problem for people who want to be in the RAF or in the US flying corps. One in four people has this, it's thought to be genetic and it tends to run in families. It's seems to be that when you have bright light going into your eyes, in those people who are susceptible, the light in some way triggers you to want to sneeze. We used to think that the light made your eyes water and the water ran down your nose, making it tickle. But it happens far too quickly for that so we think that it's actually some mis-wiring in the back of the brain that triggers your sneezing centre.