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Question of the fortnight: Why do some people sneeze when they look into the sun?

Blogging science to life

Sat 28 May 2011, Written by: Nicole

Question via twitter from @WalkSnap

Interestingly enough this is a question that has been puzzling people for centuries; even Aristole asked why the heat of the sun prompts us to sneeze and that was in 4th Century BC! The ‘photic sneeze reflex’ (‘sneezing when looking into the sunlight’ to you and me) is actually quite common - 10% of the population are photic sneezers as it is a genetic trait.

Sneezing is controlled by the parasympathetic nervous system which feeds into the part of the brainstem called the medulla oblongata. The problem which arises when trying to answer the question is that the way the nervous system coordinates a normal sneeze it is still not fully understood.

Yet there are a couple of explanations for why photic sneezing happens, it might be that nerve impulses from the different nerve endings around the nose and eye could become mixed up and the brain could get confused where the impulses came from, which would also explain why some people sneeze when they tweeze their eyebrows!

Another theory is that the nerves at the base of the medulla are a tangled web of nerve wires, when bright sunlight hits our eyes the parasympathetic system’s usual response is to constrict the pupils and so limit the amount of light entering the eye, but for some people whose medullas are wired differently sunlight triggers a different reflex – a sneeze!

Are you a photic sneezer?

If you sneeze a set number of times on exposure to light, you sneeze depending on light contrast i.e entering bright sunlight, the sneeze takes time to ‘recharge’ and if you have a close family member with a similar sneezing reaction to light – you are probably a photic sneezer!

If you are why not come out of the dark and let us know!

Thanks to New Scientist for the answer

Remember every fortnight, we are answering your science questions about the human body. It's all part of finding out how amazing you are, in the run up to the opening of our new exhibition All About Us in February 2011.