From a PopSci exploration of the science of bodily functions:
A fourth of adults have an inherited tendency to sneeze or an increased ability to sneeze around bright light, a phenomenon called the photic sneeze reflex. Some say that light-induced sneezing is a meaningless neurological quirk, but [Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond author Robert R. Provine] suggests that it evolved as a "daybreak ritual" that provides daily nasal cleansing. The fact that the photic sneeze often can’t be repeated too soon seems to support a theory of a health-promoting cleanse triggered daily by the sun (or artificial light in modern times). The benefit, however, may be offset by the dangers inherent in the closed-eyed nature of the sneeze, car crashes among them.
For more on Provine, check out Maria Popova's excerpts from his book on crying.
The Dish 