Cold sores are blistering sores typically close to the mouth. They begin with a tingling sensation and progress to clusters of painful blisters, then crusted sores that may heal with scarring. They are caused by the herpes simplex virus and are usually transmitted by direct contact (kissing, etc.). Even with treatment the virus is never cleared from the body completely. Therefore, treatment is aimed at preventing or minimizing outbreaks. This is done through oral antiviral medications such as acyclovir.