The skin consists of three layers, from the outside to the inside of the epidermis, dermis, subcutaneous tissue. 1. Epidermis: that is, the superficial layer of the skin, composed of keratinized complex flat epithelium, mainly including two types of cells, namely, keratinocytes and dendritic cells, the epidermis can be divided into five layers from the outside to the inside, that is, the stratum corneum, the transparent layer, the granular layer, the stratum spinosum, and the basal layer. 2. Dermis: located under the epidermis, containing various fibers and gelatinous substances, muscles, nerves, blood vessels, lymphatic vessels, sebaceous glands, hair follicles, sweat glands, etc. are located in this layer, the dermis can be divided into the papillary layer and reticular layer from outside to inside. 3. Subcutaneous tissue: in the lower part of the dermis, mainly composed of loose connective tissue and adipose tissue, blood vessels, lymphatic vessels, nerves, hair follicles, sweat glands, etc. can also be extended to the subcutaneous tissue, the layer can deliver nutrients to the epidermis and dermis, and can preserve energy and moderate the impact.