Final answer:
Full thickness burns lead to a lack of pain perception because they destroy the nerve endings responsible for sensing pain due to the extensive damage to the skin and underlying tissues.
Step-by-step explanation:
Because full thickness burns harm the nerve endings in the body that are essential for feeling pain, the patient is unable to feel the burns, also referred to as third- and fourth-degree burns. These burns can damage underlying muscle and bone in addition to penetrating the whole layers of the epidermis and dermis. Fourth-degree burns cause such extreme damage to the skin's entire thickness as well as the underlying tissue that the local nerve endings are destroyed. The patient no longer experiences pain in the region of the full thickness burn as a result of the loss of sensory function. This is different from less severe burns, such as first-degree and second-degree burns, which involve less damage to the skin and nerve endings, leading to pain and discomfort.