The largest organ of the human body is the skin, the weight of the skin accounts for about 16% of body weight, the thickness of the skin is 0.5-4mm, the skin area of adults is 1.5-2m², newborns are about 0.5m². The skin is the first barrier of the human body against external aggressions and has a variety of physiological characteristics and functions.1. Characteristics: Compared with other organs, the skin has more typical characteristics. The skin is divided into three layers from shallow to deep, namely, epidermis, dermis and subcutaneous tissue, mainly including epithelial tissue, connective tissue, fatty tissue, as well as nerves, blood vessels, muscles, skin appendages and many other tissues. Different races, ages, health conditions, the color of the skin will vary, the thickness of the skin of different parts of the body also varies, such as the palms of the hands and soles of the skin is thicker, while the armpits and facial skin is thinner; 2, function: the main function of the skin is to protect other tissues below the skin from external aggression, such as microbial infection, physical stimulation, chemical injury, etc., and the regulation of body temperature, feeling external stimuli In addition, the skin can also be absorbed from the outside world. In addition, the skin can also absorb a small amount of nutrients and water from the outside world. The skin is directly related to the health of the human body. If the skin is damaged by disease and not treated in time, it may cause damage to other tissues and organs, so it is very important to protect the skin.