Skin is the largest organ of human body, with a total weight of 5% ~ 15% and a total area of 1.5 ~ 2 square meters. The thickness of dermatology varies from person to person or from place to place, ranging from 0.5 to 4 mm. The skin covers the whole body and protects various tissues and organs from physical, mechanical, chemical and pathogenic microorganisms. Skin has two barrier functions: on the one hand, it prevents the loss of water, electrolyte and other substances in the body; On the other hand, prevent the invasion of harmful substances from outside. Maintaining the stability of human internal environment plays an important physiological protection function, and skin also participates in the metabolic process of human body. There are several colors of skin (white, yellow, red, brown, black and so on). ), which mainly varies according to race, age and place.

The skin consists of epidermis, dermis and subcutaneous tissue, including accessory organs (sweat glands, sebaceous glands, nails and toenails), blood vessels, lymphatic vessels, nerves and muscles.

cuticle

Epidermis is the outermost layer of skin, with an average thickness of 0.2 mm. According to the different development stages and morphological characteristics of cells, it can be divided into five layers from outside to inside.