Ever glance upward at a bright light, only to find yourself needing to sneeze?
It might surprise you that not everyone experiences this. If you’re one of those in the majority—yes, 2/3 of people do not experience this—then I’m here to explain what happens to me, in my own words.
For folks who nodded silently while reading that first question, I’ve got some goodies for you today, too. If you’re anything like me, you’ve wondered why this happens for quite some time. This question was brought to my attention by a curious reader with whom I’ve shared lots of curious questions like this over the years, and I’m grateful for the question!
This phenomenon has been dubbed Photic Sneeze Reflex, or PSR for short, although you might know it by the common term Sun sneeze, or maybe light sneeze.
As a kid, I didn’t have allergies (I somehow dodged that genetic bullet!), but I would still sneeze on occasion. Sometimes it was clear why I was sneezing, like if I caught a whiff of pepper, or if some dust tried to go up my nose while I was playing little league baseball.
More often than not, however, there wasn’t a discernable reason for me to sneeze. My nose had its reasons, and I recounted the most common ones here:
Natural Sneezasters
Every now and then, a sudden, violent event will occur, causing everyone to stop what they’re doing and take a look.
However, I was able to put two and two together eventually, and I saw that looking upward at a bright light could trigger that sneeze reflex in me. How curious!
Why should light trigger a sneeze? What kind of sense does that make?
Well, I mentioned that only about a third of people experience PSR, Photic Sneeze Response. Photic comes from the same root word as photon, and it just means “from light.” It is these tiny packets of light that are ultimately responsible for the effect.
It turns out that the optic nerve, which processes those photons as they come in, is located right next to the trigeminal nerve. When your brain seeks to gather light for information, some of that same light inadvertently strikes that nerve, which is responsible for controlling parts of your face, and that includes your nose.
If you feel that tickle that lets you know you’ve got to sneeze, it is the trigeminal nerve that is responsible for this feeling. So, if I look upward at a light (please do not stare into the Sun), I envision that some of those tiny photons go down the wrong tube, so to speak, since those tubes are pretty close together.
Sight and sound seem like they’re utterly unconnected, but the truth is that they’re both ways of us interpreting the outside world. We gather raw data by smelling or seeing, then encode it into a signal our brains can interpret, and finally process the information from out there.
The brainstem is like a hub for our senses, where all of them pass through and become useful. I find it helpful to remember that these signals all enter your body in different ways, but they all pass through this tiny region before we conceptualize them as sensations like sight or smell.
So, the next time you look up at a light and have to sneeze, think about how interconnected our senses really are! Remember that smell and sight are just the ways our brains interpret that flood of data that’s always coming in, and every now and then, the wires can get crossed.
For the other 2/3 of you, I hope this gives you a tiny window into our photic-sneezy world.
I'm a sun sneezer.
Deja vu!
I'll go ahead and repost an edited version of my comment under the "Natural Sneezasters" post:
Speaking of the "bright light making you sneeze." I've had an extreme version of this all my life. My mom still retells stories of her rolling me out onto the street in my stroller and me sneezing so hard that my pacifier would fly out. Back then, they used the term "allergic to the sun" to describe it.
To this day, stepping out into a bright light from a dark place is 90% likely to make me sneeze hard, twice. (It's almost always exactly twice.)
But it gets weirder. My wife has this too. And now, so do our kids. It's quite entertaining to watch our family step out into the sun together, only to immediately break into a sneezing fit.
I've looked this up a few years ago, and it's a legitimate thing called "photic sneeze reflex," or, more adorably, the ACHOO syndrome (I'm not making any of this up). Wikipedia says it affects between 18--35% of people. It also means I'd probably have a harder time than most people in getting certified as an airline pilot, for whom it's an elevated risk factor on account of the whole "Sneezing uncontrollably upon exiting the cloud layer while piloting a giant metal tube with hundreds of peope inside."
On the plus side, whenever I experience that annoying "want to sneeze but can't quite do it" moment, it's enough for me to look at a bright source of light to unleaseh the sneeze.