A fast-growing, dome-shaped skin tumor that usually occurs on sun-exposed areas of the body, especially the head, neck, arms, legs, and back of the hands. Keratoacanthomas often begin in a hair follicle. They may look like squamous cell skin cancer, but they are usually benign and rarely spread to other parts of the body. Keratoacanthomas are usually caused by sun exposure, but they may also be caused by a human papilloma virus infection, a weakened immune system, certain genetic conditions, exposure to some cancer-causing chemicals, and an injury to the skin. They usually go away on their own but can sometimes come back. They occur more often in older men.