The common name for blisters cause by the Herpes Simplex virus, to which 98% of the world's population has been exposed by the age of two. This is a different but similar virus to that which causes genital herpes. Cold sores often occur on the external lip (herpes labialis), and on the gum tissue near the teeth. They last from seven to ten days, and can be treated with antiviral medications when severe.
