Scars are depressions or indentations in the skin that occur after a medical condition such as acne or after a surgical incision. Especially when they're on the face or other visible areas, scars can carry the stigma of adolescent acne long after the acne is gone, or they can serve as unpleasant reminders of a past surgery.
Acne scars can occur as the skin heals from pimples, whiteheads and blackheads that form when oil, bacteria and dead cells get stuck below the skin's surface. Acne scars are typically indented marks or raised, red areas that sometimes give the skin a wavy appearance. Surgical scars, meanwhile, form naturally as skin heals from an incision.