A keloid is a scar that does not know when to stop forming, becoming large, shiny, smooth, and often pink and dome-shaped.
It is not known why some people get overgrown scars after injuries, surgery, or acne, but keloids are more common among people of black and Asian descent, so a genetic factor is suspected.
In normal scarring, after the inflammation that follows an injury subsides, scar tissue begins to form, along with tiny new blood vessels. Cells in the skin around the injury, called fibroblasts, produce collagen, a fibrous connective tissue. As more and more of the fibers link up, the scar becomes harder.
In a keloid, the process continues long after the wound is covered over, and the scar can become quite large. Keloids are not dangerous but can be disfiguring, tender, and sometimes itchy.
Removal of a keloid by surgery or the use of lasers, followed by corticosteroid injections at the site, is sometimes but not always successful, and can cause even worse scarring.
Someone with a tendency to form keloids may want to avoid plastic surgery, though doctors can sometimes use hidden incisions in facial surgery or avoid making cuts in the periphery of the face, where keloids are more likely to form.