Thursday, 19 April 2007

Sneezing in the Sun

After eight years and I am still learning new things my husband: we were walking down the street when the clouds parted, revealing a bright sun and he consequently sneezed! And now I realize that this phenomenon affects a significant number of other people I know. So in case you were ever wondering why looking at the sun on a bright day makes you sneeze here is the answer:

When a nerve cell is stimulated it passes on a chemical / 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. So, when you look at the sun or a bright light, your eyes (and their nerves) suddenly have a lot of very strong information to pass to the brain. In addition to passing on their message, they also 'leak' a bit. Part of the path for the optic nerves (from your eyes) happens to be close to your sneeze reflex and so it can be triggered by accident.
-This text was originally contributed by David Hone on Ask a Biologist

Anecdotal evidence also seems to indicate that this unusual reflex has a genetic link, so may be common among members of the same family. This is confirmed by R. Eccles of the Common Cold and Nasal Research Group who says that this phenomenon (which he terms the ‘photic sneeze’) affects between 18-35% of the population. And that the photic sneeze is a well known hazard to fighter pilots when they turn towards the sun or are exposed to flares from anti-aircraft fire.


oreneta said...

I always wanted to know that....but why does it leak? And how? Is there a factor with the depth of the mylin sheath? nerve proximity? The size of the optic nerve?


Anonymous said...

Thats all very interesting. However, as this also happens to me, I can tell you its related to muscles around your eyes and nose. When you look at the sun you squint. This causes the nose to scrunch up too and this has the effect of irritating or stimulating something inside the nose and thats what causes the sneeze.

Malacoda said...

God your English is awful. What do they teach you in those Canadian schools?

Martin said...

Have a look at our site, which is in need of updating, but where we have tried to gather as much scientific data as possible:

The proximity of the optic nerve and trigeminal nerve would certainly be a factor for those with the reflex, but there may also be something lacking in the "insulating" gel around the nerves, which explains how the signals are mixed.

Mike said...

I want to ask more questions about the subject. Oreneta, I personally can see how an electrical signal can jump from one nerve to another, I work on telephone poles. I don't know what the mylin sheath is though. My question is: Since all humans smile unless something is physically out of balance, and all humans sneeze unless something is out of balance, why is it that all other mammals sneeze but don't laugh. Furthermore, can there be a link made between humans and the rest of the mammal world through this much ununderstood phenomenon.

Anonymous said...

I was born with this, I always thought it had to do with eye sensitivity. Of course I'm much to young to understand what most of these things mean, but its interesting to learn about.

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