scar, fibrous connective tissue that forms at the site of injury or disease in any tissue of the body. Scar tissue may replace injured skin and underlying muscle, damaged heart muscle, or diseased areas of internal organs such as the liver. Dense and thick, it is usually paler than the surrounding tissue because it is poorly supplied with blood, and although it structurally replaces destroyed tissue, it cannot perform the functions of the missing tissue. Scar tissue may therefore limit the range of muscle movement or prevent proper circulation of fluids when affecting the lymphatic or circulatory system. Extensively scarred tissue may lose its ability to function normally.

Huáscar, d. 1533, Inca of Peru; son of Huayna Capac. At his father's death (1525) he became emperor, but had to share the empire with his younger half brother, Atahualpa. Shortly before the beginning of the Spanish conquest under Francisco Pizarro, Atahualpa rebelled successfully and later secretly ordered Huáscar murdered.

Mark left on the skin after a wound heals. Cells called fibroblasts produce collagen fibres, which form bundles that make up the bulk of scar tissue. Scars have a blood supply but no oil glands or elastic tissue, so they can be slightly painful or itchy. Hypertrophic scars grow overly thick and fibrous but remain within the original wound site. Scars can also develop into tumourlike growths called keloids, which extend beyond the wound's limits. Both can inhibit movement when they result from serious burns over large areas, especially around a joint. Scars, especially those from unaided healing of third-degree burns, can become malignant. Treatment of serious scars is one of the most important problems in plastic surgery.

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