Between 18-35% of people sneeze when exposed to bright light, especially sunlight. This is called the photic sneeze reflex, and it's caused by crossed signals between the trigeminal nerve (which controls sneezing) and the optic nerve.
Why Does Sunlight Make Some People Sneeze?
Step outside on a sunny day and achoo! For millions of people, bright light triggers an uncontrollable sneeze. It's not allergies, and it's not in their heads. It's a genuine neurological quirk called the photic sneeze reflex.
Scientists estimate that 18-35% of the population experiences this phenomenon. If you're one of them, you've probably noticed it your entire life without knowing it had a name—or that not everyone shares your sunny sneezes.
Your Brain's Wiring Mix-Up
The culprit is a case of crossed signals in your nervous system. When bright light hits your eyes, it stimulates the optic nerve. This nerve runs remarkably close to the trigeminal nerve, which controls sensations in your face—including the sneeze reflex.
In people with the photic sneeze reflex, the intense signal traveling along the optic nerve "leaks" into the neighboring trigeminal nerve. Your brain interprets this as nasal irritation and triggers a sneeze, even though nothing is actually tickling your nose.
It Runs in Families
The photic sneeze reflex is genetic. If one of your parents has it, you have about a 50% chance of inheriting this quirky trait. Scientists have traced it to a dominant gene, which is why it often passes directly from parent to child.
The technical name? Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome—deliberately abbreviated as ACHOO. Yes, scientists have a sense of humor.
More Than Just Sunlight
While sunlight is the most common trigger, other bright lights can set off the reflex too:
- Camera flashes
- Bright indoor lighting
- Looking at snow or white sand
- Emerging from a dark room or tunnel
The key factor isn't the light itself but the sudden change in brightness. Your eyes adjusting from dark to light creates the strongest neural signal—and the most reliable sneeze.
A Minor Inconvenience with Real Consequences
For most people, sun sneezing is just a quirky party fact. But it can pose genuine risks in certain situations. Fighter pilots, for instance, are screened for the photic sneeze reflex. A sudden sneeze during a high-G maneuver or while looking toward the sun could be dangerous.
Some surgeons also report that bright operating room lights can trigger unexpected sneezes—not ideal when you're holding a scalpel.
No Cure, No Problem
There's no treatment for the photic sneeze reflex, and frankly, most people don't want one. It's harmless, mildly amusing, and gives you something interesting to share when someone catches you sneezing at the sun.
If you want to minimize the effect, sunglasses help. By reducing the intensity of light hitting your eyes, you reduce the neural signal that triggers the sneeze. But for many sun-sneezers, those first few bright-light sneezes of the day are just part of life—a small reminder that human biology is wonderfully, weirdly imperfect.