Quote:
'About 25% of people do actually sneeze when exposed to bright lights like the sun. We do not know exactly why this happens, but it might reflect a "crossing" of pathways in the brain, between the normal reflex of the eye in response to light and the sneezing reflex. There is no apparent benefit from "sun-sneezing", and it probably is nothing more than an unimportant (but annoying) holdover of evolution...
In the pupillary light reflex, shining a light in the eye causes nerve signals to go from the eye to the brain and then back the eye again, telling the pupil to constrict. In the usual sneeze reflex, tickling the nose causes nerve signals to go from the nose to the brain and then back out to the nose, mouth, chest muscles and everything else involved in the actual sneeze. The key point is that the nerve signals take complicated routes through the brain, but usually the pupillary light reflex and sneeze reflex take different routes. Apparently what happens in sun-sneezers is that shining a bright enough light in the eye ALSO sends nerves signals from the eye to the brain and then back out to the nose, mouth and chest.'
Because I hate it when people aren't informed about these things. Sorry for being a nerd. :D