Keloid

Keloid: A scar that doesn't know when to stop. When the skin is injured, cells grow back to fill in the gap. Somehow, they normally "know" when the scar tissue is level with the skin, at which point the cells stop multiplying. When the cells keep on reproducing, the result is a what is called a overgrown (hypertrophic) scar or a keloid -- a tough heaped-up scar that rises quite abruptly above the rest of the skin. It is irregularly shaped and tends to enlarge progressively.