2 min read

Autosomal Dominant Compelling Helio-ophthalmic Outburst

morning sun
Triggered by the morning sun. Photo by Mohamed Hassan from Pixabay

AKA, a "sneeze"

(P.S. Have you ever noticed how doctors give even the simplest things the most complicated names!)

I know, I know...you can make fun of me, but offer me a glimpse of bright sunlight in the morning and I'm going to start sneezing!

I've had this response to sunlight all my life and have never thought twice about it. But I recently decided to research this question and I learned that this is an inherited trait that affects about a quarter of all people.

And so, we say "achoo!" Public Domain Picture from Pixabay

Sneezing is most often a response to irritation in the nose, and it's an effective way for our bodies to quickly expel foreign particles that can irritate or infect our nasal passages.

Did you know that sneezes produce around 40,000 droplets that are forcibly blown up to 26 feet! This is what makes sneezes a potent health risk, and it's why you should sneeze into a handkerchief, or the crook of your arm. At the very least, look downward so the droplets are sent towards the ground, instead of outward into the air that other people are breathing.

Each sneeze generates a plume of airborne droplets. Photo by James Gathany - CDC Public Health Image library ID 11162

But why do some people sneeze in bright sunlight? It's the same sneeze, but with a wildly different trigger.

This response is called photic sneezing, or autosomal dominant compelling helio-ophthalmic outburst (abbreviated ACHOO), and people have been wondering about it since Aristotle wrote about it in 350 BCE.

But there's still no obvious explanation for what causes photic sneezing.

My favorite theory is that because optic nerves lie in close proximity to nerves running from the nasal cavity to the brain, it's possible that the buzzing of nerves triggered by bright light tickles the same nerves that make us sneeze. And, as someone who experiences this phenomenon, this is exactly what it feels like.

trigeminal nerve
Trigeminal nerves from our nose and eyes pass in close proximity to each other enroute to the brain. Illustration from John Charles Boileu Grant, An Atlas of Anatomy

Whatever the cause, I was thankful to discover in my research that sneezing in response to bright light is no cause for alarm, it's just something that some of us lucky people get to do!

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