The skin can be divided into three layers. The external layer is called epidermis, the second layer true skin (dermis, corium), and the third subcutis. A strong connection and interdependence exists between these layers. Hair, nails, sweat and sebaceous glands are called skin appendages.

The epidermis is made up of five different layers. In the basement membrane new skin cells are constantly being made, which migrate to the skin's surface. There they die off and form, in the shape of dead cells, the external horny skin layer. The layer of horny skin continuously loses cells due to scaling, while new cells are continuously produced in the epidermis' germ layer. Apart from skin cells, the immune system's defence cells and various skin receptors that are responsible for the skin's senses, as well as pigment cells producing the skin's pigments, are to be found in the epidermis.

The epidermis is followed by the true skin, which is the dermis. The dermis is made up of two layers. The upper layer is made up of loose connective tissue. In contrast, the so-called net layer is criss-crossed by firm connective tissue fibres, made up of collagen and elastin. The blood vessels in the true skin layer see to the skin's supply with nutrients. Nerve fibres, lymphatic vessels, sebaceous glands and sweat gland channels traverse this layer. The true skin is responsible for the skin's elasticity and thus also for the formation of wrinkles in old age.

Apart from loose connective tissue, subcutaneous fatty tissue is to be found in the subcutis. The size of fat cells depends on the nutritional condition. Hair roots and sweat glands are also anchored here, and larger blood and lymphatic vessels criss-cross this layer. The fatty tissue also serves as heat-isolator, protective layer and energy reservoir.

The mucous membranes, in contrast, are made up of non-horny, one or many-layered epithelial tissue and the connective tissue lamina propia lying below. The mucous membrane in the gastrointestinal tract is complemented by a thin muscle layer.