Most scientists believe that looking at the sun makes you sneeze because the cranial nerves run very close to one another inside the head.
When a stimulus as bright as the sun comes into the optic nerve through the eye, it stimulates a reflex reaction in the nearby olfactory nerve, triggering a sneeze.
A portion of the population will sneeze every time they look toward the sun; a larger portion can help a sneeze along with sunlight.
It gets more bizarre: Some people begin sneezing from the stimulation of a full stomach; some, from combing their hair; others, from tweezing their eyebrows or cleaning their ears with a cotton swab.
Aside from the dangers of a comb or Q-Tip injury, there’s no apparent harm from this cross-nerve stimulus.