Scars are areas of fibrous tissue (fibrosis) that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound (e.g., after accident, disease, or surgery) results in some degree of scarring. An exception to this is animals with complete regeneration, which regrow tissue without scar formation.
Scar tissue is composed of the same protein (collagen) as the tissue that it replaces, but the fiber composition of the protein is different; instead of a random basketweave formation of the collagen fibers found in normal tissue, in fibrosis the collagen cross-links and forms a pronounced alignment in a single direction.
This collagen scar tissue alignment is usually of inferior functional quality to the normal collagen randomized alignment. For example, scars in the skin are less resistant to ultraviolet radiation, and sweat glands and hair follicles do not grow back within scar tissues.
Scar formation depends on many factors that influence wound healing, which are important to bear in mind because most of the negative factors involved can be stopped by implementing an adequate treatment.
see Peridural scar.