How does skin cancer affect the body?

Skin cancer begins in the cells that make up the epidermis -- the top layer of skin. When the DNA that controls the cells' growth is damaged, it causes an overgrowth and buildup of skin cells. Eventually, this skin cell buildup forms a tumor, which results in the symptoms you see, such as irregular spots, red bumps, or scaly patches on your skin. Skin cancer most commonly affects areas of skin that are exposed to the sun but may develop almost anywhere on the body, including underneath fingernails and in the genital area. If left untreated, skin cancer can grow deep into the skin and spread through the rest of the body, causing serious complications.