An upper respiratory infection, also known as the common cold, is one of the most common illnesses and can be the result of more than 200 different viruses. Of course, your best defense when it comes to cold and flu season (or anytime you don't wish to get sick) is to wash your hands as often as possible. Certainly before touching your face or eating. But you can also kick your immune system into high gear, raising your defenses even further, with just a few simple techniques.