Like all cancers, skin cancer happens when your body’s cells grow uncontrollably. These abnormal cells can metastasize or spread. With skin cancer, this out of control growth happens on your skin’s outer layer called the epidermis. These cancerous cells can form bumps, scaly patches, or tumors. The most common skin cancers happen on areas of your body that are frequently exposed to the sun, like your ears, your neck, the back of your hands.