The outer skin layer, or epidermis is normally 0.2 millimetres thick. The main function of epidermis is to protect the body. Epidermis can be subdivided into the horny layer, the middle layer, and the basal layer. Epidermis is constantly renewed as cells from the basal layer divide, and move up to the surface of the skin and shed off. This procedure takes about 1 month.
Most factors affecting the condition, and ageing of the skin take place in the upper dermis. The dermis is made up of connective tissue (collagen, elastin), and ground substance which give the skin firmness, resilience, and maintain its suppleness. Collagen and elastin are in this respect especially important. The dermal cells producing both collagen, and elastin are called fibroblasts. The number and activity of these cells decrease by age, or by severe physical damage to the skin. The diminished activity in dermis results in thin, slack, and wrinkled skin. This is called the ageing of the skin. The thickness of the skin varies being thinnest in the face, neck, and inside of the arms. This is where the ageing is the most visible.