About 1 in 4 people sneeze when they step into bright sunlight.

The Photic Sneeze Reflex is scientifically known as Autosomal Dominant Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome. It is estimated to affect between 18% and 35% of the global population. This phenomenon occurs due to 'crosstalk' between the optic nerve, which senses light, and the trigeminal nerve, which controls facial sensations and sneezing.When a person with this trait is exposed to sudden bright light, the intense signal traveling along the optic nerve overstimulates the nearby trigeminal nerve. The brain's somatosensory cortex misinterprets this electrical surge as an irritation in the nasal lining. Consequently, the body initiates a sneeze to clear a perceived irritant that is not actually there.Research published in the journal 'Nature' and studies by the University of Zurich have confirmed that the trait is hereditary. It follows an autosomal dominant inheritance pattern, meaning if one parent has it, their child has a 50% chance of inheriting the reflex. While usually harmless, it can pose risks for pilots or drivers who experience sudden glare.Historical records show that even ancient philosophers like Aristotle and Francis Bacon observed this phenomenon. Modern genetic testing companies like 23andMe have identified specific genetic markers on chromosome 2 that are strongly associated with the photic sneeze response. This makes it one of the most easily identifiable and common genetic quirks in human biology.