Final answer:
Skin grafts are required for full-thickness (third-degree) and fourth-degree burns due to the extensive damage to skin tissue that cannot heal on its own.
Step-by-step explanation:
Skin grafts are necessary for full-thickness burns, which are also known as third-degree burns.
These burns extend through the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function.
A fourth-degree burn is even more severe, with damage to the underlying muscle and bone as well.
Both of these types of burns cannot heal on their own as the local tissues required for repair are damaged.
Medical procedures like excision or debridement, followed by grafting of skin from an unaffected part of the body, are essential for recovery.