The skin is one of the largest and most important organs of the body, all skin accounts for 4% to 6% of body weight, together with subcutaneous tissue for 15% to 17% of body weight. The skin has five functions: (1) mechanical protection and defense function: ① skin is the most important natural barrier of the human body, good softness, protection against external light friction, impact and pull; ② regulate the evaporation of body fluids to prevent a large loss of water in the body; ③ skin is weakly acidic (pH 5.5), not conducive to the invasion and reproduction of bacteria, viruses, fungi. (2) Respiratory function: In 24 hours, 3~4 grams of oxygen are absorbed through the human skin (except the head). At 30°C, human skin breathing accounts for 1% of the entire gas exchange. While in a hot environment, heavy physical labor, increased air oxygen concentration, or in a high pressure environment, the skin’s gas metabolism accounts for 15-20% of the lung gas metabolism. When engaging in physical labor under the same temperature conditions, the efficacy of oxygen absorption through the skin is increased by 50% to 100% compared to the resting state. Therefore, there is no doubt that patients with large burns should increase the gas exchange of the lungs. (3) The function of regulating body temperature: The skin contains a large number of cold, heat, pain, touch and other complex receptors, a rich network of blood vessels and 2.5 million sweat glands, with an average secretion area of 1080 square meters. The skin regulates body temperature by dissipating and insulating heat. The way of heat dissipation is mainly radiation and sweating, sweating heat dissipation accounts for 21% of the total body heat, and when a lot of sweating, up to 75%-95%. Skin vasoconstriction and subcutaneous fat can reduce heat dissipation and maintain body temperature, thus achieving the role of regulating body temperature. (4) Immune function: The skin has thymus-like effects, immature immune T cells are stored through the skin and released for bleeding after maturation. Skin Langheim cells have C3b receptors with antigen integration and antigen amplification: subcutaneous keratinocytes secrete interleukins. Its functions are to cause fever and inflammation, promote wound healing, induce into interleukin II, mediate the conversion of lymphocytes to synthesize IgG, promote autoimmune function, etc. (5) Blood storage function: Under normal conditions, part of the skin blood vessels are in a semi-constricted state, and can accommodate 1000 ml of blood if expanded. In the blood vessels around the burn wound and tissues, which are all expanded due to the inflammatory response, the blood storage capacity will be greatly increased. Therefore, the skin also has the name of blood bank.