Cold sores are annoying and painful fluid-filled blisters. They are also called Fever Blisters or Herpes simplex. They often break out around the lips and sometimes under the nose or around the chin. Cold sores can be very contagious. Once a person is infected with primary herpes, the virus stays in the body and causes occasional attacks. An attack can follow a fever, sunburn, skin abrasions, or stress. Cold sores usually heal by themselves in a week. Over-the-counter anesthetics can provide some relief, and prescription antiviral drugs may reduce these kinds of infections.