Why Do You Sneeze When You Look into the Sun?

Nothing is worse then when you are on the brink of a sneeze, but you can't get it out! My solution has always been to look up into the sun to force a sneeze.. but why does that work?! This has been wondered about for centuries, but modern neurobiology might have the answer.

Aristotle was one of the first to try and answer this question. He surmised that it must be the heat of the sun responsible for the phenomena in "Book of Problems." About 2,000 years later, Francis Bacon tested this theory with the observation that when you look at the sun with your eyes closed.. the heat remains but there is no sneeze. This led him to conclude that the sun in your eyes made them water.. causing moisture to seep into your nasal cavity.

These theories were educated and rational for the understanding of science during those time periods, but as we learned more about neurobiology/ human physiology it was deemed that Bacon's theory was disregarded due to the speed of the sneeze following the sun exposure and a new theory was born. This new theory was deemed as a result of 'crossed wires' in the facial neural networks (cranial nerves).

The cranial nerves are a complicated part of the nervous system that comes out of the brain stem (connects spinal chord to the brain and contains the medulla oblongata, pons and midbrain). There are twelve cranial nerves and they control a variety of functions from blinking to hearing to smelling (etc). These nerve tracts run very close to each other and it is theorized that when the signal of excessive light enters your pupils the sudden increase in electrical current traveling from the optic nerve (signaling to constrict the eyes pupil) accidently triggers the trigeminal nerve confusing the brain into thinking there is a irritant in the nose- causing a sneeze.

This has come to be called the photic sneeze reflex, but does not seem to be linked with any further medical problems. It also seems that this doesn't happen to every person. Further research into a genetic element of this reaction has began due to it's potential to shed light into other neurological conditions. (Shining light into the eyes of someone with epilepsy can trigger a seisure, and it could be related to the cross wiring of the cranial nerves) So when you can't seem to sneeze, look into the sun and see if you are part of the population that undergoes the photic sneeze reflex.