MedlinePlus: Herpes Labialis
Overview of the common infection which is characterized by small and usually painful blisters on the skin of the lips, mouth, gums, or the skin around the mouth.
Fever Blisters and Canker Sores
Describes the symptoms, treatment, and differences between these two common disorders of the mouth. From the National Institutes of Health.
Netdoctor.co.uk: Cold Sores
Explains the symptoms, how to prevent cold sores, and how they are treated.
MayoClinic: What are Cold Sores?
Also called fever blisters. Includes information on symptoms, complications, prevention, and self care.