Sneeze on the cusp? There's a one-in-four chance this will work for you. Evasive sneezes have got to be one of the most irritating afflictions, but for some of us, there can be a simple solution. In the case of photic sneezing, simply looking at a bright light can be enough to elicit a satisfying sneeze. The reason is due to pupil dilation, the nervous system, and a fun little acronym in ACHOO Syndrome. The photic sneeze reflex (PSR) is also known as Autosomal Dominant Compelling Helio-Opthalmic Outburst Syndrome, but given life is too short for using so many long words, we prefer ACHOO Syndrome. It’s characterized by uncontrollable sneezing in response to sudden exposure to a bright light, such as leaving a dark cinema and staring at the sun. It’s unusual because sneezing is typically linked to pathogens or irritants, like the good old pepper gag, so why would light make someone sneeze? ACHOO Syndrome doesn’t affect everyone and is genetic, believed to be linked to the genes rs10427255, near ZEB2, and rs11856995, near NR2F2. Around one in four of us can encourage a sneeze by looking at a bright light when our noses are already tingling, and in this case it can actually be a real relief. “It’s not a disease,” neurologist and human geneticist Louis Ptáček from the University of California, San Francisco told PBS NewsHour. “Some people find it annoying, but some people like it to some extent. They’ll say, ‘It helps me get a sneeze out.’” Pure photic sneezing, on the other hand, is thought to be far less common. This means that even when there’s no irritation in the nose at all, a person will uncontrollably sneeze when exposed to bright lights. In these cases, it can actually be dangerous as a light-induced sneezing fit while driving can cause an accident. Sneezing has even featured in automatism cases where drivers have claimed they lost control due to the involuntary act of sneezing, but its success rate as a legal defense varies considerably. As for what causes ACHOO Syndrome, it’s possible people with the right genotype have an irregularity in their trigeminal nerve, the fifth and largest of the cranial nerves. According to the University of Nebraska Medical Center, the trigeminal nerve provides sensation in the face, but it also picks up on any irritation inside the nostrils and triggers a sneeze in response. It’s possible, then, that a bit of cross-wiring here could see our sneezes become a little confused. A suggested mechanism behind ACHOO Syndrome suggests that sudden exposure to a bright light causes our pupils to constrict, sending a nerve signal that in some people might accidentally excite other nerve pathways, including the one that secretes mucous into the nose. This could be picked up as an irritant, triggering a sneeze in the typical way. So, next time you find yourself struggling to bring a sneeze to fruition, try staring at a bright light. There’s a one-in-four chance it could work for you. Source
