What causes a SNEEZE?!?!?

I'm not a Doctor so I might be completely wrong here, but there are a number of things that cause people to sneeze such as bright light, eg looking up in the sky on a bright day, dust and pollen, hair and pets, and colds. I think sneezing is the bodies way of removing dust particles and irritants that are in the body. People sneeze differently possibly because of different shaped canals in the nasal passage, some may be wider, allowing more air to pass, some people try to control their sneezing so as not to spread their germs so far and that may result in different intensities of the sneeze. I guess different sneezing is just a logical extension of differences between people.