Schematic diagram of herpes simplex virus.
Cold sores are small blisters that develop on the lips
or around the mouth. They are caused by the herpes simplex virus and
usually clear up without treatment within 7 to 10 days. You may not have any symptoms when you first become infected
with the herpes simplex virus. An outbreak of cold sores may happen some
time later.
Cold sores often start with a tingling, itching or burning sensation
around your mouth. Small fluid-filled sores then appear, usually on the edges
of your lower lip.