What causes cold sores on the lips not to go away?

Cold sores are...: Ulcers caused by a viral infection. If you have a single ulcer that does not go away you need to be sure it is not a cancer. If you have multiple ulcers that do not resolve you probably have an immune system issue. This may be as simple as chronic stress or something more serious. You should probably see your doctor.

Reinfecting: Although cold sores and canker sores are often confused for each other, they are not the same. Cold sores, also called a fever blister or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, cold sores are caused by a virus and are extremely contagious. Also, cold sores typically appear outside the mouth -- usually under the nose, around the lips, or under the.