The skin is located on the surface of the human body and is the first line of defense of the body, especially the stratum corneum, which has a very important function. From the perspective of weight and area, the skin is the largest organ of the body, its weight accounts for about 16% of body weight; the area of the skin is 1.5 – 2m2 for adults and about 0.21m2 for newborns. The thickness of the skin varies from person to person and varies from part to part, usually 0.5 – 4mm (excluding the subcutaneous fat layer). The skin of children is much thinner than that of adults; the skin of the limbs and trunk is thinner on the extensor side than on the flexor side; the skin of the posterior occipital, collar, buttock and palmoplantar areas is the last; the skin of the eyelids, vulva and breast is the thinnest.