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Why can a third-degree burn be painless despite severe tissue damage?

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Cross-section diagram of human skin showing burn depth by degree, with arrows indicating that first-degree burns affect only the epidermis, second-degree burns reach the dermis, third-degree burns extend into subcutaneous tissue, and fourth-degree burns penetrate to muscle. — burn This diagram shows how burn injuries are classified by severity. First-degree burns damage the outer skin, known as the epidermis. First-degree burns are the least severe form of burn injury. Second-degree burns damage the outer skin and some of the underlying skin, known as the dermis, which also includes some connective tissue. Third-degree burns damage all the layers of skin, including subcutaneous tissue. Fourth-degree burns, which are the most severe, destroy every layer of skin and also damage muscle, tendons, and bones.

A third-degree burn, also known as a full-thickness burn, is often painless because the injury destroys the entire thickness of the skin. This process obliterates the sensory nerve endings located within the dermis, which are responsible for detecting and transmitting sensations of pain, heat, and touch to the brain. Because these receptors are physically destroyed along with the surrounding tissue, they are no longer capable of generating or sending pain signals.1