When we step outside into bright light with other people, we can occasionally hear someone sneezing. Is this merely a coincidence? Or is there a possible explanation for this? It turns out that this desire to sneeze after looking at an abrupt bright light occurs in about a third of the world’s population.
Photo of a man sneezing. Author: James Gathany via Wikimedia Commons
This surreal way of sneezing is called photic sneeze reflex, or, conveniently, ACHOO (Autosomal dominant Compelling Helio-Ophthalmic Outburst) syndrome. Despite being highly prevalent around the world, we know very little regarding this phenomenon. In fact, a study has found that victims of this reflex think this occurs in everyone, whereas “normal” people become bewildered when finding about its existence. This level of unawareness might be due to the little threat that this condition poses to those who have it.
Youtube user: Thomas Denton
Due to the common occurrence of this condition within a family, it is generally regarded as an autosomal dominant trait, which simply means that it is likely for an affected parent to have an affected child. This is surprising, since the sneeze that we are all familiar with is acquired from environmental factors like viruses, regardless of how we are genetically shaped.
So how is it then that the sun or any other light sources trigger sneezing? Many theories were considered, with the first one dating back to Aristotle’s time. He speculated that the sun’s heat had a direct effect on the nose, causing it to become irritated and therefore induce sneezing. Clearly, this hypothesis was refuted later on, because the sneeze disappears if you close both eyes.
The most supported reasoning behind this involves the cranial nerves, particularly the optic and the trigeminal nerves. It is our trigeminal nerve that is primarily responsible for sending information that leads to sneezing to the brain. However, the complexity and the compactness of our heads allow this nerve occasionally picks up signals from the optic nerve. Thus, when some of us look at a bright light that stimulates the optic nerve, it is erroneously translated by the brain as the body’s need to sneeze.
Here is a video that gives a very simplified explanation:
Youtube user: 2ManyVid3os
As I mentioned before, this condition is generally harmless to those who have it. However, it can still pose serious risks in certain situations. For example, it is common for drivers to get a sudden outburst of sunlight shone onto their eyes. Two-thirds of the population would squint their eyes and pull down the sun visors. The remaining third on the other hand, would experience an uncontrollable movement caused by the photic sneeze reflex. Considering that they are driving, you can imagine how dangerous that can be.
Although you may find it hard to believe, there is a perk to inheriting this condition. I am sure that all of us had a moment where we had a desire to sneeze, but was not able to produce it. However, this is not a problem for around 2.3 billion people, including myself, since we can deliberately produce a sneeze. Besides, who wouldn’t want to feel elevated, given that a sneeze is 1/8 of an orgasm?
-Sanggi(Daniel) Hong
