In May 2001, the Sixth National Academic Conference on Burn Surgery was held in Hangzhou, China. This conference changed the division of burn depth from the original three degrees and four divisions to four degrees and five divisions. The main difference is to divide the original three degrees into three degrees and four degrees. The details are as follows: four degrees and five divisions: the burns are divided into one degree, shallow second degree, deep second degree, third degree and fourth degree. (The main difference is the division of the third degree into third and fourth degrees.) First-degree burns: The lesions are the lightest. It is generally an injury to the epidermal stratum corneum, hyaline layer, and granular layer. Sometimes the spiny layer can be injured, but the hair growth layer is still alive, so the regeneration ability is active. It often heals within a short period of time (3-5 d) without leaving a scar. Superficial second-degree burns: Injuries that include the entire epidermis up to the hair growth layer, or the papillary layer of the dermis. The regeneration of the epithelium depends on the epithelial proliferation of the remaining hair growth layer and skin attachments, such as sweat ducts and hair follicles. In the absence of secondary infection, healing usually occurs after 1-2 weeks and no scarring is left. Sometimes there are prolonged pigment changes. Deep second-degree burns: Include dermal damage below the papillae layer, but some dermis remains. Because of the residual dermis, there is no need to implant the skin, and the wound can heal on its own. The wound can heal on its own. After healing, a scar is often left. If there is no infection, the healing time usually takes 3-4 weeks. If you’ve got an infection, not only is the healing time prolonged, but in severe cases the skin attachments or epithelial islets can be destroyed, and the wound can only heal with a skin graft. Third-degree burns: the entire skin is damaged, and the epidermis, dermis and its attachments are all destroyed. Fourth-degree burns: deep into the muscles and even bones, internal organs, etc. In the early stage, deep fourth-degree injuries are often covered by the burned and unexfoliated skin, which is not easily identified clinically. Since the skin and its accessories are all destroyed, the wound surface has no source of epithelial regeneration, wound repair must rely on skin implants and flap transplants, and in severe cases, amputation must be performed.