A cold is a viral infection that affects the upper airway including the nose, pharynx, throat and lung airways. Introduction to Colds The common cold is the most common reason that people miss work or school. There are at least 200 different viruses that cause colds. These are known as. These are not the same viruses that cause the flu. Colds are very contagious. They are airborne and transmitted when one coughs, sneezes and then touches an object after they have sneezed on their hand or blown their nose. Anyone can get a cold. Children tend to get more colds than adults do. The reason adults get fewer colds is that they have become immune to particular viruses that cause the cold.