Have you ever walked outside, took one look at the bright morning sun, and immediately started sneezing? You may’ve wondered if this sudden batch of sneezes might have something to do with your allergies, but (spoiler!) it’s actually a totally unrelated condition.
Feeling confused yet? That’s why we’re about to demystify the photic sneeze reflex (a.k.a. “sun sneezing”).
If looking at the sun or other bright lights makes you sneeze, you’re part of the 18-35 % of people who experience something called the photic sneeze reflex—uncontrollable bursts of sneezing in response to bright light. The condition is also called “sun sneezing” or autosomal dominant compulsive helio-ophthalmic outbursts of sneezing (ACHOO) syndrome (no, really). For unknown reasons, the condition is more common among women than men.
So you can rest assured that you’re not the only person who gets hit with a bout of sneezing when they forget their sunglasses. And if you’re wondering why exactly this happens, you’re not the only one—scientists don’t have the answer to that question figured out yet.
But even though the root cause of the photic sneeze reflex has yet to be discovered, the phenomenon has been observed long enough for people to notice a few prevailing trends—like the consistent symptoms.
The most recognizable symptom of photic sneezing reflex is right there in the name—sneezing. It can also come along with watery eyes or a feeling of tenderness around your nose.
If you also have allergies, you might be curious about how you can tell the difference between this reflex and allergen-induced sneezing. Your first clue will be whether or not you’ve looked at any bright lights recently, because the photic sneezing reflex kicks in pretty much immediately after the eyes register a shift from darkness to light. (It’s actually the change in intensity of light that provokes the reflex, which is why standing out in the sun all day won’t result in you spending hours sneezing non-stop.)
The other key hallmark of photic sneezing reflex is the number of sneezes. This number varies from person to person, but not from episode to episode—meaning that if you sneeze three times in a row when you look at a bright light one day, you won’t only sneeze once the next time you do that.
So if you head outside on a cloudy day when pollen counts are high and sneeze once or twice, that’s probably your allergies talking rather than photic sneezing reflex.
As you know by now, the exact cause of photic sneezing reflex is still unknown. But that doesn’t mean that doctors don’t have theories about why it happens. There are also some known risk factors (not that photic sneezing is usually dangerous) that make it more likely that you’ll have the condition.
If you experience photic sneezing reflex, there’s a good chance many of your relatives do too. In fact, the reflex runs in families so often that scientists think that you may only need one parent who has it to inherit it, making it a dominant trait.
As we mentioned earlier, the most popular theory right now is that the photic sneezing reflex occurs in response to a change in the intensity of the light around you, rather than any specific level of brightness. That could be because your nervous system makes your pupils contract in response to sudden bright light (to protect your eyes from damage), and may in the process accidentally activate the sneeze response in your nose.
Theories aside, you may be more likely to be sensitive to light in other contexts if the sun makes you sneeze.
While the photic sneezing reflex isn’t thought to be some kind of allergic reaction to the sun, studies have shown that the same antihistamines used to treat allergies make people less likely to sneeze in response to light. That might suggest some kind of common underlying cause, but we’ll need more research to know exactly what that is.
Even though researchers still have a lot to learn about the photic sneezing reflex, the bottom line is that the condition is usually harmless, apart from the annoyance of having to get through two or three sneezes before carrying on with your day.
That said, you should be careful about driving or operating heavy machinery outdoors if you know you have the photic sneezing reflex. Remember, it’s all about the shift in light intensity, so as long as you always have a pair of sunglasses handy, this condition shouldn’t get in the way of your bright future.