MD A cold is a viral infection that affects the upper airway including the nose, pharynx, throat, airways, and lungs. 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 include rhinoviruses and coronaviruses, and they are different from the viruses that cause the flu .
Cold viruses are very contagious.
They are airborne and are transmitted when one breathes, coughs, or sneezes. Cold viruses can be spread when a person with a cold sneezes into his or her hand or blows his or her nose and then touches an object. Cold viruses can live for up to 3 hours on a surface such as a doorknob or toy. Colds are caused by rhinoviruses and coronaviruses. Children generally have 6 to 8 colds a year, but they may get as many as 12 if they live in a family with school-age children.