Mental Floss

Why I Sneeze in Sunlight

By Chris Higgins

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Growing up in Florida, I had a weird allergy: the sun. Walking outside, coming from from a typically cool, dark indoor place, I'd invariably sneeze -- sometimes twice. It happened to my father too, causing a strange family multi-sneeze spectacle whenever we'd leave a movie. For me it was just one or two sneezes, then all better. What caused this? I always assumed there was something about bright light that disagreed with my bookish, "indoor kid" nature. Apparently I was right; today I learned that science indeed has an answer: this phenomenon is called the photic sneeze reflex, and according to Wikipedia it "affects 18-35% of the human population." So my Dad and I aren't alone.

According to Scientific American, the photic sneeze has long been a subject of curiosity, going all the way back to Aristotle. Francis Bacon even tested the phenomenon in the 17th century by stepping outside with his eyes closed -- no sneeze. Hmm. So why would exposure to bright sunlight affect the nose? According to Scientific American:

A sneeze is usually triggered by an irritation in the nose, which is sensed by the trigeminal nerve, a cranial nerve responsible for facial sensation and motor control. This nerve is in close proximity to the optic nerve, which senses, for example, a sudden flood of light entering the retina. As the optic nerve fires to signal the brain to constrict the pupils, the theory goes, some of the electrical signal is sensed by the trigeminal nerve and mistaken by the brain as an irritant in the nose. Hence, a sneeze.

These sneezes even have a ridiculous acronym to describe them: ACHOO, "Autosomal-dominant Compelling Helio-Ophthalmic Outburst." Photic sneezes may also be related to migraines and seizures brought on by bright or flashing lights. Go figure.

Are You a Photic Sneezer?

If so, speak up in the comments!

(Via FitSugar.) Photo by Flickr user quinnums, used under Creative Commons license. You can read a bit more flossy writing about sneezing here: Do people sneeze in their sleep without waking up?