When skin or organs are damaged, the body naturally wants to heal itself. Since the body cannot re-create healthy skin or tissue, it puts together new fibers that are not as functional as the original tissue, but that serve as a protective, useful barrier. When this barrier is completely healed, it is known as a scar.

Scar tissue is the fibrous connective tissue which forms a scar; it can be found on any tissue on the body, including skin and internal organs, where an injury, cut, surgery or disease has taken place, and then healed. Thicker than the surrounding tissue, scar tissue is paler and denser because it has a limited blood supply; although it takes the place of damaged or destroyed tissue, it is limited in function, including movement, circulation, and sensation. Other than with minor cuts and scrapes, scarring is a common result of any bodily damage.

Scar tissue in the skin is inferior to healthy, normal skin for several reasons: sweat glands are damaged or destroyed, hair does not grow back, and there is less resistance to ultraviolet radiation. Skin scars are normally flat and pale, illustrating the history of the injury which caused them, yet often a body will produce too much fibrous tissue, resulting in an extra thick or raised scar.

Hypertrophic scars form as red lumps on the skin but stay within the confines of the original wound. Keloid scars may cover the original wound but then continue to grow, causing a type of tumorous growth. Hypertrophic and keloid scars can occur in anyone, but are more common in younger and dark skinned people. In rare cases, keloid scars form without warning or injury.

Scars can never be completely removed. Many doctors advise their patients to use vitamin E supplements or creams to speed the healing process and keep the scar tissue suppler. Surgeries are available to remove scars, but any surgery will always make a new scar: the former scar may be less obvious, but it will not go away completely. Surgery is not recommended for hypertrophic or keloid scarring, as there is the risk of recurrence and worse scarring.