For some people, looking directly into the light can trigger a sneeze, either helping them force out one that won’t come, or catching them completely off guard. Between 18 and 35 percent of the population carries the gene for the photic sneeze reflex, or as it’s called by some clever otolaryngologists, Autosomal dominant Compulsive Helio-Ophthalmic Outbursts of sneezing (ACHOO).
Why on Earth we have evolved this bizarre reflex is still a mystery. Animals sneeze to enhance their ability to smell, so it’s possible that there is some rudimentary protective adaptation at work here. Or, it’s just a weird quirk we keep passing through the generations.
MORE: Ask A Scientist: Why Does Light Make You Sneeze?