You can develop a keloid scar (a scar that is harder and smoother, with raised tissue that is pink, red, or darker, than usual with normal scarring) from surgery, body piercing, or just scarring from accidental injury.
A minor cut can result in keloid scarring, while the same type of cut on another part of the body, or happening at another time, might result in a normal scar.
Some cultures encourage keloid growth on scars as decorative or symbolic skin adornment.
Keloid growth can extend beyond the scar site. It is mostly collagen; keloids are not cancerous or pre-cancerous and are not contagious. Keloids can occasionally be itchy or painful.