Light microscope of a keloid scar. A keloid is an enlarged scar that grows beyond its original boundaries. It can itch, cause pain or be tender to the touch. Keloids consist of a mass of collagen, a tough fibrous protein, that forms as a result of a defective healing process. After a period of time most keloids flatten and cease to itch. Treatment, if required, is usually by re- excision and radiotherapy.