When treating severe burns and trauma, skin regeneration can be a matter of life or death. Extensive burns are usually treated by transplanting a thin layer of epidermis, the top layer of skin, from elsewhere on the body. However, this method not only leaves large scars, it also does not restore the skin to its original functional state. Unless the dermis, the layer below the epidermis, which contains blood vessels and nerves, is regenerated, it cannot be considered normal living skin.