It is more about signal leakage between neurones. The optical nerve is closed to the one controlling sneezing so when the optical is highly excited, it can activate the sneezing nerve.
Source : I have a friend with this and he looked it up once
this post was submitted on 01 Jun 2025
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That's the prevailing theory, yes, but as far as I've found there's not empirical evidence to back it up. The theory does make perfect sense to me, though!
Also, as a sufferer, I've noticed it almost always requires sunlight or something with close to the same frequencies. Most artificial lights don't trigger it *for me.
Artificial lights absolutely trigger it for me. They just have to be bright.
"Bright" is kind of a spectrum though. Sometimes a light is just bright enough that you can trigger a sneeze, but only if you focus on it. Other times that same light will almost trigger a sneeze with focus, but not go completely over the edge. That's a very annoying feeling when that happens.
Interesting! I'll update my post, it makes sense there would likely be variability in how it presents due to biology. My experience isn't necessarily the default.
TIL. I've heard a similar thing about certain smells being closely tied with the memory centre in the brain.
Out of all of our senses, smell is the one that triggers memory the quickest. The olfactory nerves in your nose are extremely sensitive and have a direct line to the long term memory part of the brain
I have this and it's annoying but has the best name.
It's known as ACHOO syndrome. Autosomal Dominant Compelling Helioopthalmic Outburst.
Contrived acronym. I much prefer Photic Sneeze Reflex, it's easier to remember and doesn't sound like bullshit 😂
I have no research to back this up, but I think it's just a glitch that isn't detrimental to passing on one's genes, so the trait got to stay around. Not everyone has it.
But if I were to hypothesize an evolutionary benefit, maybe it is a good thing to sneeze out all the fungal spores from your cave once you emerge. But then again, if it was important, shouldn't this also induce coughing?
Closes your eyes when you stare at the sun?
No! I will burn out my retina and there's nothing you and big sunglass can do to convince me otherwise!
Not every trait has an adaptive significance.
I always assumed it was a hold over from a rodent-like ancestor. Stick your nose out of a barrow, and you want to clear it to get a good sniff of the environment.
It's definitely one of those effects that confuses people. If you don't do it, it seems weird as hell. If you do, it seems weird that some people don't get it.
Its a glitch.
Its important to understand that evolution does not "design" anything with intent or purpose. Its all chance and survival of the fittest does select for traits that confer greater survival.
But plenty of traits are neutral or minimally negative in their survival benefits so also suriviveor develop. And it only affects traits that impact reproducing and passing on traits to the next generation. So many traits may be totally unaffected by evolutionary pressures as they have no relevance to survival of the fittest.
Plus the other species being competed woth over time and the environment generally shape what traits are desirable versus detrimental.
Basically not everything has an evolutionary purpose or function.
Ok, but: you describe what glitches are in detail, which wasn't the question. OP clearly understands the concept behind evolution, despite using imprecise terminology.
You seem confident that there's no benefit to the light/sneeze reflex: why? Is that an authoritative answer, or just your opinion? Do we know the mechanism behind the reflex, and can we trace it to an origin, like the recurrent laryngeal nerve?
Wait what? I don't recall doing this. Or do you mean squinting instead of actually sneezing?
No, sneezing, as in the photic sneeze reflex. If I look at the sun by accident I'll sneeze.
Known as the "suntzu"
Bless you
Or as my kids started calling it "Daddy is allergic to the sun"
TIL ! Wow
Only some people get this reflex (me for e.g.). It's an actual sneeze.
Maybe it's a thing that only certain people do, like rolling your tongue. Looking at a bright light doesnt make me sneeze, and until just now I thought it was just an old wives tale, like remedies for curing hiccups. Doesn't work but widely believed.
Yeah, it's definitely a real thing, it's fairly common even
But if you don't have it, you don't have it, so looking at bright lights isn't going to help you sneeze
Come visit Disney with my family this fall. You'll see me and my kid both sneeze every time we step into the Florida sun after leaving a slightly darkened show build.
Oh I'd love to, if only I could afford it