Keloid scars are firm, smooth, hard growths due to spontaneous scar formation. They can arise soon after an injury, or develop months later. Keloids may be uncomfortable or itchy, and may be much larger than the original wound. Keloids may form on any part of the body, although the upper chest and shoulders are especially prone to them.
The precise reason that wound healing sometimes leads to keloid formation is under investigation but is not yet clear.
While most people never form keloids, others develop them after minor injuries, burns, insect bites and acne spots. Dark skinned people form keloids more easily than Caucasians.
Keloids are harmless to general health and do not change into skin cancers.
As wounds heal, scar tissue forms, which at first is often red and somewhat prominent. Over several months, a scar usually becomes flat and pale. If there is a lot of tension on a healing wound, the healing area is rather thicker than usual. This is known as a hypertrophic scar.