Some of you probably know it. It is a lovely day, warm with the sun shining from a blue sky, but then suddenly out of blue you sneeze violently for one or two times. I have experienced it often when going out in the sun or sitting in the bus when it turns and exposes me to direct sunlight. I wondered if I suffered from some kind of sun allergy, but on the other hand I only sneezed a couple of times max and was then fine. What could possibly be the reason?

The other day while reading an old issue of Research*eu (no 54, Dec 2007), I finally found a possible explanation.

The magazine has a short article on the photic sneeze reflex or ACHOO (autosomal dominant compelling helio-opthalmic outburst), which is a gene mutation that results in an error in the trigeminal nerve, a nerve that leads sensory information from the face into the brain. As the name indicates, three nerves meet in the trigeminal nerve, the ophthalmic nerve, the upper maxillary nerve and the mandibular nerve. The error means that a powerful stimulation of the ophthalmic nerve, which is stimulated by sudden change of light, also results in a stimulation of the upper maxillary nerve, which is other stimulated by irritation and blockage of the nose.

So in other words, I sneeze violently because sudden sunlight due to an error instructs my brain that my nose is blocked and requires a sneeze. Well, now I am not completely calm knowing that I have a mutation in the nerves of my brain, but the article does not mention any other side effects and between 11% and 36% of us all, furthermore, have the gene mutation.