scar

Scars (cicatrices) are areas of fibrous tissue (fibrosis) that replace normal skin (or other tissue) after injury. A scar results from the biologic process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. An exception to this is animals with regeneration, which do not form scars and the tissue will grow back exactly as before.
Scar is not identical to the tissue that it replaces and is usually of inferior functional quality. For example, scars in the skin are less resistant to ultraviolet radiation, and sweat glands and hair follicles do not grow back within scar tissue.