"Hey doc, why do we sneeze?"

Good question but I think I've got the answer on this one. Sneezing is something all of us do and it's usually associated with a cold or allergies.

It starts as an irritation to the nasal and respiratory passages, which means you might also sneeze after you inhale something your nose doesn't like—pepper, for instance.

Here's what happens: Your nose senses an invader lurking inside—mucus, pollen, pepper.

It sends an s-o-s to the brain, which activates a violent reflexive response.

The result is dramatic: Your chest muscles suddenly compress your lungs, sending a blast of air rocketing upwards. Simultaneously the opening between your throat and your mouth slams shut, forcing the air to shoot out through your nose.

All of this is accompanied by a loud sound that's known by pretty much the same word in every language—a-choo!

Sneezing is also a great way for germs to spread themselves around, so I'm sure you don't need me to remind you what your mother always said: Cover your mouth when you sneeze!