Doctor Oz was asked by a lady, why does your nose run in cold weather? I have always wondered this as well! The worst is when it is so cold outside that your nose is running, and you cannot even tell!
Dr Oz said that cold weather paralyzes the cilia or small hairs on the surface of your nose, which move the mucus to the back of your throat normally. When these tiny hairs are paralyzed, your nose runs more. Dr Oz also said that one of the main reasons we breathe through our nose is so that the air is not too hot or too cold and to clean the air.