* Full-thickness burns may extend into the subcutaneous tissue, meaning the skin can't heal on its own. These burns, classified as third- and fourth-degree burns, are caused by prolonged exposure to chemicals, electrical current, flame, hot liquids, or tar. The skin appears dry, waxy, white, leathery, or hard. Thrombosed vessels will be visible, and muscles, tendons, and bones may be involved. Signs and symptoms include lack of pain, possible hematuria, possible entrance and exit wounds from an electrical burn, and shock. Skin grafting is often required for healing, and patients may lose function of extremities or digits, or need amputation.