Keloids are raised overgrowths of scar tissue that occur at the site of a skin injury. They occur where trauma, surgery, blisters, vaccinations, acne or body piercing have injured the skin. Less commonly, keloids may form in places where the skin has not had a visible injury. Keloids differ from normal mature scars in composition and size. Some people are prone to keloid formation and may develop them in several places.
Keloids are more common in African-Americans. They are seen most commonly on the shoulders, upper back and chest, but they can occur anywhere. When a keloid is associated with a skin incision or injury, the keloid scar tissue continues to grow for a time after the original wound has closed, becoming larger and more visible until it reaches a final size. They generally occur between 10 and 30 years of age and affect both sexes equally, although they may be more common among young women with pierced ears. Keloids may form over the breastbone in people who have had open heart surgery.