Final answer:
A fourth-degree burn is where both the skin and subcutaneous tissue are destroyed, affecting the underlying muscle and bone, requiring serious medical attention.
Step-by-step explanation:
In the classification of burns, the type of burn in which the skin and subcutaneous tissue are destroyed is known as a fourth-degree burn. A fourth-degree burn is the most severe form, extending through the full thickness of the skin and affecting the underlying muscle and bone. This level of burn damage is extensive and cannot be repaired by the body alone; it often requires medical interventions such as excision (debridement), amputation in severe cases, and possibly skin grafting. Unlike first-degree burns, which affect only the epidermis, or second-degree burns, which involve the epidermis and part of the dermis, fourth-degree burns also impair the nerve endings, which can paradoxically result in less pain initially due to nerve damage.