The tendency of some people to sneeze in response to bright light wasn't only just noticed in the last century; the Greek philosopher and scientist Aristotle observed the phenomenon as well. In his Book of Problems, he (or possibly his students) asked, "why does the heat of the Sun provoke sneezing, and not the heat of the fire?" He concluded that the Sun's heat aerosolises the fluids within the nose, which triggers a sneeze. The heat of a fire, on the other hand, not only vaporises those fluids, but also consumes them, thus drying out the nose, which actually inhibits a sneeze.

Never mind that he wasn't exactly spot on either in the cause for the sunny sneeze – it's light, not heat – nor in the explanation, but it means that the reflex was known to some perhaps as early as the third century BC.

Bright lights, big sneeze

We now know quite a bit more about the biology that underlies the photic sneeze reflex. For example, the reflex is now also known by the hilariously apt acronym Achoo, which stands for Autosomal Dominant Compelling Helio-opthalmic Outburst. "Autosomal" because the affiliated gene is located on one of the non-sex-linked chromosomes, and "dominant" because you only need to inherit it from one of your parents to express the trait.

In 2010, a group of geneticists led by Nicholas Eriksson of the genetic testing company 23andMe identified two single nucleotide polymorphisms, or SNPs, that were associated with the sunny sneeze by assessing the genotypes of nearly 10,000 23andMe customers. These SNPs are alterations to single letters within a person's genetic library. One is called rs10427255 and the other, about which there is somewhat less statistical certainty, is called rs11856995. One of them is located nearby a gene known to be involved in light-induced epileptic seizures, which raises the possibility that there might be some kind of biological link between the two syndromes.