Chris Smith, of Kings High School, asks :-
Why do we close our eyes when sneezing? Is it because otherwise our eyes may fall out?
Ian Stewart, an ear, nose and throat surgeon at Dunedin Hospital, responded.
There is certainly no risk that eyes could fall out during sneezing!
Eye closure during sneezing is almost certainly a reflex. Reflex is an automatic movement over which the body has no conscious control. For example if you burn your hand, your hand is jerked back automatically out of further harms way before you even think about it at a conscious level.
A sneeze is caused by intense stimulation of the fifth cranial nerve which supplies both the inside of the nose and sensation around the eye. Your eyes are closed by the seventh cranial nerve. The course of the two cranial nerve lies very close in the brain and obviously stimulating the fifth nerve intensely can cause the eyes to close. A reverse effect is seen when sneezing occurs in response to bright sunlight.
What I have said probably explains some of the mechanics of how it happens but it does not really answer your question "why?". We shall be thinking and possibly experimenting a little further on this now you have raised the question. You have raised a question for which science cannot provide a complete explanation. This is very interesting, because it is by raising questions like this that science advances. If we do come up with a better explanation we shall be in touch with you but please don't hold your breath too much.