Most sneezes make sense. Dust, pollen, or a cold tickles your nose, and out it comes. But some people swear they sneeze at the oddest things: stepping into sunlight, finishing a big meal, or even biting into a piece of dark chocolate. Is any of that real?
Here's the honest answer. Sneezing after chocolate is something you'll hear about, but we couldn't find solid scientific evidence that chocolate is a recognized trigger. Several other unusual triggers, though, are well documented. The most famous is the photic sneeze reflex, sneezing at bright light, which affects an estimated 18 to 35% of people. Another is sneezing after a very large meal.
The Sunshine Sneeze
If you've ever walked out of a dark building into bright sunshine and immediately sneezed, you're far from alone. This is the photic sneeze reflex. It's also nicknamed ACHOO syndrome, a playful acronym for "Autosomal-dominant Compelling Helio-Ophthalmic Outburst."
It's inherited, passed down in families. Interestingly, it seems to be triggered by a sudden change in brightness rather than by any particular color of light. Exactly how it works still isn't well understood.
To see why light could matter, it helps to know how a sneeze works. Normally, an irritant in the nose sets off nerve signals that travel along the trigeminal nerve to the brainstem. The brainstem then fires off orders to muscles in the chest, belly, and throat to blast air out. Your eyelids even squeeze shut on their own.
A Puzzle for Over 2,000 Years
People have wondered about this for a very long time. Around 350 BC, the Greek philosopher Aristotle asked, "Why does the heat of the sun provoke sneezing?" He guessed that the sun made the inside of the nose sweat.
In the 1600s, English philosopher Francis Bacon tested that idea by facing the sun with his eyes closed. He didn't sneeze, so he figured the eyes must be involved. He thought sunlight made the eyes water and the moisture tickled the nose. Scientists later ruled that out too, because the sneeze happens too fast for watery eyes to be the cause.
The Big-Dinner Sneeze
A rarer trigger is a very full stomach right after a large meal. It even has a name: snatiation, a mix of sneeze and satiation, the feeling of being full. Like the sunshine sneeze, it's considered a genetic trait passed down in families.
Other reported triggers include a sudden drop in temperature or a breeze of cold air. Some people with the photic reflex even sneeze when they get an injection near the eye during eye surgery.
Sneezes, Superstition, and Safety
Sneezes have always fascinated us. In ancient Greece, they were seen as signs from the gods. In 401 BC, when the Athenian general Xenophon gave a rousing speech to his soldiers, one of them sneezed at the end, and the troops took it as a good omen.
Most odd sneezes are harmless annoyances. But a sudden sneezing fit can be risky while driving or flying, especially for people sensitive to bright sunlight. If you notice a pattern that worries you, or a new symptom after eating, talk to your doctor.
And remember to sneeze into your elbow or a tissue, since sneezes can spread germs. Whether it's the sun, a holiday feast, or that mysterious chocolate bar, at least now you know you're in good company.
