Up to 35% of people sneeze when exposed to bright light, a genetic trait first noted by Aristotle.

The photic sneeze reflex is scientifically known as Autosomal Dominant Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome. It affects between 18% and 35% of the global population and is inherited in a dominant pattern. This means if one parent has the reflex, their child has a 50% chance of inheriting it as well.Aristotle first pondered this phenomenon in 350 BCE in his work 'The Book of Problems.' He questioned why the heat of the sun caused people to sneeze. However, modern research conducted by institutions like the University of Zurich has debunked the heat theory. Scientists now focus on the proximity of the optic nerve to the trigeminal nerve within the brainstem.When a person moves from a dark environment to bright sunlight, the optic nerve sends a massive electrical signal to the brain to constrict the pupils. Because the trigeminal nerve is located so close to the optic nerve, the brain sometimes misinterprets this signal. It perceives the light stimulus as an irritation in the nasal cavity instead.This neurological 'cross-talk' results in a sneeze to clear the perceived irritant. While usually harmless, the ACHOO syndrome can be dangerous for pilots or drivers who experience sudden glare. Studies published in the Journal of Human Genetics continue to explore the specific SNPs, or genetic variations, that cause this unique sensory overlap.