Although their cause is unknown, many researchers have attempted to identify an infectious agent, and some suspect an as yet unidentified member of the Herpesvirus family. Canker sores usually begin with a tingling or burning sensation, followed by painful, red spots or bumps which ulcerate, forming open sores, often in clusters. Their centers appear white or yellow, and they are often surrounded by raised, reddened edges. After 4 to 7 days or so, they become covered with gray-colored membranes, and are less painful. Complete healing may take an additional 1 to 2 weeks.
Recurrence is frequent and almost universal.
Uncommonly, canker sores are accompanied by more generalized systemic symptoms as fever, malaise, fatigue and swollen lymph nodes. In this setting, canker sores are clinically indistinguishable from the lesions of Herpetic stomatitis, an illness of infants and young children clearly caused by Herpes Simplex Virus. Unlike Herpes, however, canker sores do not seem to respond to antiviral medications and they do not seem to be contagious. Prolonged or severe mouth ulcers may be a sign of other problems as well, such as allergic drug reactions and dermatologic diseases like pemphigoid, lichen planus and rarely squamous cell carcinoma. Usually, however, the vast majority of canker sores are pretty clearly garden-variety canker sores and require no special evaluation or treatment.