Something that has always appalled me for as long as I can remember is why I sneeze every time I step out into the sunlight. In fact, I’m not the only one asking this question. According to scientificamerican.com, Aristotle pondered the same strange occurrence in The Book of Problems asking, “Why does the heat of the sun provoke sneezing?” (Looking).
Turns out, we still don’t know. In the 17th century, another curious English philosopher named Francis Bacon decided to step outside with his eyes closed in order to refute Aristotle’s idea that heat on the nose causes sneezing. Bacon experienced heat on his nose, but he didn’t sneeze. Now it was believed that when sunlight hit the eyes it caused the eyes to water which sent moisture into the nose and irritated it.
However, our current understanding of physiology makes this explanation impossible. Our tear ducts are too slow and the sneeze happens too quickly. Although we don’t have an exact answer to this pressing question, we have some sort of idea of what may cause sneezing in sunlight. This sneezy sensation is termed photic sneeze reflex and today experts believe it may all be linked to the crossing of wires in the brain.
The most recent theory suggests that the trigeminal nerve, which causes you to sneeze, is accidentally triggered when the optic nerve, which is very close to the trigeminal nerve, is signaled, thus causing a sneeze. The optic nerve pics up changes in lighting, which explains the suns role in photic sneeze reflex.
So why don’t we know more about this topic? My guess is that this isn’t harmful to humans so there would be very little funding, or interest, to back up an experiment of this kind.
It looks like we’ll still be in the dark about the causation of photic sneeze reflex. But until there’s a better answer, don’t forget your tissues on a sunny day.
“Looking at the Sun Can Trigger a Sneeze.” Scientific American Global RSS. N.p., n.d. Web. 19 Sept. 2014. <http://www.scientificamerican.com/article/looking-at-the-sun-can-trigger-a-sneeze/>.