So Mrs. McFarland, my Advanced Biology teacher in high school was wrong - there actually IS a reason I sneeze whenever I walk from indoors to outdoors and into direct sunlight. Sneezing as the result of being exposed to a bright light—known as the photic sneeze reflex—is a genetic quirk that is still unexplained by science, even though it has intrigued some of history's greatest minds, and affects anywhere from 1/10 to 1/3 of the population.
It happens to me, especially when the sun is very strong and it is warmer than 80F degrees. Mrs. McFarland said there was no such thing. And perhaps back then, nothing had been proven. And even now, it's all really speculation. All I know is, I'm pretty consistent about doing it.