Why does light make me sneeze?

12 March 2019

RUNNY-NOSE

A child with a runny nose and sneezing into a handkerchief

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Question

Why do I sneeze when I see a bright light?

Answer

Jake wanted to know why some people sneeze when they see bright lights. Chris Smith asked Cambridge physiologist Sam Virtue to explain... Turns out our panel were all familiar with the phenomenon!

Sam - Well, this question is intriguing to me because I one of them. And this is a well described phenomenon, it's called the photic sneeze reflex or, because scientists are funny - autosomal compelling helio ophthalmic outburst or achoo. So this is a classic science joke...

Chris - Is that real? Is that what they really named it?

Sam - Yes they really did that. Essentially, it's the phenomenon that when we stare at a bright light we sneeze. So why this happens, we are not a hundred percent sure. But there are other examples of this, essentially, it's a bit of mis-wiring whereby your body has one sensation or one stimulus and it results in something strange happening. One way its thought possibly happen is the nerves that are essentially responsible for sneezing are also the same nerves which go to our eyes, or the trigeminal nerves.

But actually, I just thought it was a thing that happened but it actually has a couple of major issues. So the first one is fighter pilots, if they are flying into land on an aircraft carrier and its late evening, the whole sea will be lit up as a brilliant shimmering light and they will sneeze if they have this,which will quite possibly result in them crashing into the sea.

Chris - When you're doing a few hundred kilometres an hour, not much margin for error.

Sam - Yup! The Navy came up with an extremely high-tech to this - aviator sunglasses. Yeah, wear some shades and you're no longer have as much light.

But the one it's really terrifying, and I'm not sure if this is safe to say before the watershed because it makes me cringe so badly, is if you are undergoing eye surgery which requires a needle to be put into your actual eyeball they use a sedative called propofol, and the combination of propofol and putting the needle into your eye will trigger this. So surgeons doing this will generally insert the needle and then withdraw it because if you sneeze violently with needle in the middle of your eyeball... yeah.

Chris - Should have gone to Specsavers.

Sam - Yeah.

Chris - Adam?

Adam - I'm gonna shudder for a moment about the eye thing. But how common is this because if you do it and I do it as well so is that very common thing?

Chris - And I do it as well. That's three others out of... You Ljiljana?

Ljiljana - Yeah, yeah.

Chris - Tim, are you sneezer?

Tim - I don't what you're talking about.

Sam - Okay. So we're slightly over-represented here but it's thought to affect between 18 and 35 percent of the population, so it's certainly not rare.

Things that make it worse, for example, and particularly trigger it, I actually used to think it was alcohol was one of them because I would suffer this...

Chris - From personal experience?

Sam - From personal experience. But it turns out that just product of Cambridge having lots of dark, old men pubs because some transitions from dark dim lit areas to brightly lit areas will trigger it particularly powerfully.

Chris - I found it really useful this. You know when you have that horrible thing that happens to you and you want to sneeze but you can't? Well, because I have this and I know this, I facilitate a sneeze that I want to get out by looking at a bright light. And your nodding, Adam, do you do the same trick?

Adam - It makes me look really weird but it's really helpful.

Chris - Stare at the bright light and then achoo, off you go and it feels so much better.

Ljiljana?

Ljiljana- I just wanted to tell you actually Sam, I discovered this a few years ago. I didn't have it before so it's something that developed relatively recently. So it's an interesting fluke of nature, of biology.

Chris - Another weird one, people who stick things into their ear to clean it out, about 2 and a half to 3 percent of the population develop a cough reflex because there’s Arnold nerve in your ear with a cotton bud you will you will get a coughing fit. And many people who have they think they’re totally mad - you’re not, you’re just about one in 50 who have this.

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