Hypertrophic scars take the form of a red raised lump on the skin, but do not grow beyond the boundaries of the original wound, and they often improve in appearance after a few years.
Keloid scars are a more serious form of scarring, because they can carry on growing indefinitely into a large, tumorous (although benign) growth.
A keloid is a firm to hard, irregularly shaped, thickened overgrowth with claw like projections. It may be asymptomatic or painful, tender and pruritic (itchy).