Why do I sneeze sometimes when I look at the sun?

Zoe,

You have asked one of my all-time favourite bits of biology trivia and I am delighted to have got here first to answer it. However, the answer is rather complicted, so bear with me!

First off, your sneeze is what we call a 'reflex' action. It is an action that you cannot control (you can't make yourself sneeze, like you can stick your tongue out). When your nose is stimulated by something that irritates it (like pepper) the nerves send a message to the brain where the sneeze reflex set of nerves send a message to your lungs to make you sneeze and flush out the nose.

When nerve cells are stimulated they pass on a chemical and electrical message to the next nerve cell in the chain. However, if it is a very strong message, this might also leak out and stimulate nearby nerve cells. You can probably now see where this is going.....

So, when you look at the sun or a bright light, your eyes (and their nerves) suddenly have lots of very strong information to pass to the brain. So in addition to passing on their message, they also 'leak' a bit. Part of the path for the optice nerves (from your eyes) happens to be close to your sneeze reflex and so it can be triggered by accident.

So, when you look at the sun, you eyes accidently trigger a sneeze. I hope that's clear for you.

Last edited by David Hone (16th Feb 2007 14:27:18)