Oberhaut

Oberhaut, the German term for epidermis, is the outermost layer of the skin in humans and many vertebrates. It forms a protective barrier between the body and the external environment. The epidermis is primarily made up of keratinocytes organized into four layers in thin skin: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum; thick skin includes an additional stratum lucidum between granulosum and corneum. The epidermis is avascular and relies on diffusion from the underlying dermis for nutrients and oxygen. Keratinocytes originate in the basal layer and migrate outward, undergoing differentiation and keratinization, with a typical turnover time of about 28 days in healthy adults.

In addition to keratinocytes, the epidermis contains melanocytes, which produce pigment; Langerhans cells, which participate in immune defense; and Merkel cells, which contribute to light touch sensation. Functions of the epidermis include forming a barrier to pathogens and preventing excessive water loss, as well as providing some protection against ultraviolet radiation through melanin in pigmented individuals.

Developmentally, the epidermis derives from the ectoderm during embryogenesis and is anchored to the underlying dermis by a basement membrane and intercellular junctions. Clinically, damage to the epidermis occurs in burns and inflammatory skin diseases, and abnormal epidermal thickness is a feature of various conditions and aging.

Etymology: Oberhaut is the German term for epidermis; in English, the standard term is epidermis.