Cold sores. Cold sores/fever blisters are cause by the herpes simplex virus. There are 2 types—oral & genital. Either type can cause a "cold sore" although the oral type is usually involved with lip lesions. There are several otc treatments to lessen symptoms, but prescription anti-viral meds work better to clear the lesions. Herpes, however, is not cured; it is suppressed & can reappear.—>.
Herpes Virus . In many cases these are caused by the herpes virus.