There's a good reason your parent tells you to cover your mouth when you sneeze or cough! When an illness is contagious, it means one person can catch it from another. By covering your mouth when you sneeze or cough, you can prevent bacteria and viruses from getting in the air. It's also important to wash your hands, whether you are sick or well, to prevent the spread of germs on objects that other people will touch. Some contagious sicknesses that kids get are colds, the flu, and chicken pox.