I knew someone had to be looking at this, but nobody really knows why approximately one in four people (including me) experiences photic sneeze response; that is, sneezing when the sun gets in one’s eyes. There have been several different theories about why this reaction exists, and several of them have been considered and abandoned over the years, and at this point (largely because there are so many other things to look at), this particular “mystery” remains largely unsolved.

And that’s kind of the beauty of science – it’s all about observation and drawing conclusions based on that observation and experimental evidence, and can end up being kind of messy. Nothing is ever truly certain, in the sense that no idea is immune to criticism. Sure, there are some things science is pretty damned certain about, but at the same time, “certainty” only goes as far as the available evidence. Learning and understanding is never over, and our understanding of the universe is always developing and deepening based on our cumulative experience.

I actually kind of find that idea comforting. But, back to the sneezing:

I kind of like the current theory that the optic nerve crosses close enough to the trigeminal nerve (the one that causes sneezing), and occasionally overloads it, causing sternutation (sneezing): I’m fond of the fact that this little weird genetic artifact that causes me to sneeze violently when I go outside on a sunny afternoon is essentially the same as the electrical wiring problem I once had with a car – the wiring arrangement was such that the occasional hard left turn would bump two wires against each other, resulting lots of things lighting up on my dash that weren’t supposed to. It really shines a light on how weird and haphazard evolution sometimes is; that the human body isn’t any more intelligently designed than a poorly-engineered mid-90s coupe.

My personal wrinkle is that the whole photic sneeze reaction is related to eye color – I’ve never known someone without blue eyes to experience it (though one only has to go as far as the comments on the article linked to find anecdotal evidence of brown-eyed people doing it…so much for that theory!).