Cold sores (also called fever blisters, herpetic lesions, and herpetic mouth ulcers) are caused by the virus Herpes Simplex. There are two variants which cause the initial infection with herpes labialis, HSV-1 and HSV-2. Initial infection can be asymptomatic or may present as areas of small sores on the attached gingival tissues. Afterward, the virus becomes dormant, inserting itself into nerve pathways (dermatomes) of the skin.
Reactivation of the virus may be caused by periods of stress, exposure of the skin to excess sunlight or other ultraviolet light sources such as tanning lamps; or by medical/dental procedures in or around the mouth. Generally HSV-1 is responsible for repeated outbreaks of Herpes labialis. Oral reinfection by HSV-2 is rare.
Outbreaks of herpes labialis are often preceded by a prodrome (early symptoms) that may include itching or tingling. If treated during the prodromal stages with appropriate antiviral medication, progression to the stage where blisters form can often be avoided. Once sores have begun to form, the condition is harder to treat. Herpes labialis can be a painful condition. Fortunately, it will resolve on its own, and the sores generally heal within ten days to two weeks, with the peak of blister ulceration occurring around one week.
Herpes labialis is very contagious, and is one of the most commonly occurring skin lesions. About 75% of adults have the condition, which is not curable. It is spread through direct skin contact, or through oral secretions. Transmission may occur even when no skin lesions are present.