Cold sore is a virus infection that affects the lips. A cold sore is a form of the disease herpes simplex. Cold sores generally spread from one individual to another by direct contact. They frequently accompany common colds and infectious diseases, such as pneumonia and diphtheria, that are characterized by fever. For this reason they are often called fever blisters.
Cold sores appear as clusters of small blisters that contain a clear, watery fluid. When the blister is ruptured, it appears yellowish, dry, and crusted. Cold sores last from 10 to 14 days. Although the virus is unaffected by antibiotic treatment, complications caused by bacterial infections may be prevented by the application of antibiotic ointments.