No one knows why keloids form. Although most persons never form keloids, others develop them after minor injuries or even after insect bites or after acne bumps resolved.
Keloids may form on any part of the body, although the ears, jawline, neck, upper chest, upper back and shoulders are especially prone to keloid formation. Although anyone can form a keloid, persons with darker skin form them more easily than those with lighter skin, and may develop them in several places. Keloids never turn into skin cancer.