Have you ever walked outside to a beautiful day, looked up at the sun and immediately started sneezing? Maybe it happens when you leave a dark movie theater on a sunny day. Or, maybe it doesn’t happen to you at all. You’ve probably heard that if you look directly at the sun, you’ll sneeze. And let’s be honest, you’ve probably also tried it. So, did it work? It turns out a large number of people have a reflex reaction to the sun that causes them to sneeze!

This sun-sneezing phenomenon has a name. It’s actually a recognized condition known as the photic sneeze reflex (PSR). It’s also referred to as ACHOO syndrome.

Yes, I said ACHOO!

It stands for Autosomal Dominant Compelling Helio-Ophthalmic Outburst. (Say that five times fast). The condition affects up to 33% of the United States population. Of those who experience sun-induced sneezing, 67% are female and 94% are from Caucasian backgrounds. The trait is partially genetic, so if mom and dad have it, you might too.

So What Causes ACHOO?

The truth is, there aren’t very many scientific studies on the subject. It’s often seen as a funny quirk rather than a debilitating illness. Still, the leading theory says that a case of the solar sneezes might be caused by a minor glitch in the trigeminal nerve.

The trigeminal nerve is one of the largest cranial nerves. It carries sensory information down different branches across the face and under the eye, nose, mouth and jaw. Sneezing abnormalities are caused by stimulation to the trigeminal nerve terminal in the nasal cavity’s mucous-making membrane.

People with ACHOO or PSR might have a few wires crossed in this area, when it comes to their nerve network. This could cause inadvertent signals to be sparked across when they technically shouldn’t be. According to this theory, bright light causes the pupils in the eyes to constrict. This nerve signal then “accidentally” excited the nerve pathway. This prompts a flow of mucous in the nose, just a few centimeters away. The mucous flow could be mistaken by the brain as an irritant, which leads to a sneeze.

If you aren’t on board with that theory, there are others. One theory suggests that solar sneezing is an evolutionary relic from over cavemen ancestors. When they lived in a dusty caves with smoky fires burning, a sneeze when heading outside could have helped clear their airways from dust and other pathogens.

Feel free to make up your own theory about why looking up at that big thing in the sky makes our eyes watery and sends us into a fit of sneezes. Personally, the fact that the phenomenon is referred to as “ACHOO” just made my day.

Check out the video below for more info!

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