Keloids are dense, fibrous tissue nodules typically found at areas of previously traumatized skin (eg, burns, lacerations, incision scars), or arising spontaneously on normal skin. Lesions may be single or multiple. Over weeks to months, these large nodules can become painful, tender, pruritic, and grow to become very large (up to 30 cm). They can cause chronic discomfort, be disfiguring, and restrict normal tissue motion. Most patients start developing keloids in their 20s.

Keloids can affect individuals of any race and ethnicity. There is likely a genetic basis for the tendency to develop keloids, and research is ongoing.

A distinction should be made between a keloid and a hypertrophic scar. All trauma that involves the dermis will heal with a scar; however, in certain individuals, the scar is much larger and thicker than what is considered normal. These lesions are termed hypertrophic scars. In contrast to keloids, hypertrophic scars are always preceded by trauma and are always confined to the margin of the wound. Hypertrophic scars also appear immediately after trauma and show a tendency to gradually regress, whereas keloids can be delayed in appearance and are thought to very rarely spontaneously resolve.