Is skin a tissue or an organ?

The skin is generally considered an organ. It is usually composed of three layers: subcutaneous tissue, dermis and epidermis.

1. Subcutaneous tissue: usually includes loose connective tissue and adipose tissue below the skin, connecting the skin and muscles, the dermis above and the fascia and muscle aponeurosis tissue below. Fat cells are clustered into lobules. The fat septa usually contain blood vessels, lymphatic vessels, nerves, and eccrine sweat gland tissue, including apocrine sweat glands. It can connect and buffer mechanical pressure, store energy, and maintain body temperature.

2. Dermis: It is usually composed of fibroblasts, fibers and matrix, and contains blood vessels, lymphatic vessels, and other cellular components. Mast cells, macrophages and dendritic cells in the superficial dermis can interact with each other and regulate each other through cytokines, playing an important role in the activation, proliferation and differentiation of immune cells.

3. Epidermis: usually includes keratinocytes, melanocytes, Langerhans cells, etc. Melanin can buffer external mechanical damage and resist the invasion of microorganisms. Melanin secreted by cells can usually protect the skin. It is also an effect of the immune response. The organ can actively participate in initiating and regulating skin-related immune responses. The Langerhans cells inside are an important immune cell.