Cold sores are small blisters that develop on the lips or around the mouth. They’re 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.
The herpes simplex virus is responsible for cold sores. There are two strains, known as HSV-1 and HSV-2.