peau

Peau, or skin, is the outer covering of the body in humans and many animals. It serves as a protective barrier against mechanical injury, pathogens, and dehydration, and participates in thermoregulation, sensation, and metabolic functions such as vitamin D synthesis.

Structurally, the skin consists of three main layers: the epidermis on the surface, the dermis beneath it, and the hypodermis (subcutaneous tissue) below. The epidermis is mainly keratinocytes, with layers including the stratum corneum; melanocytes, Langerhans cells, and Merkel cells are also present. The dermis contains connective tissue, blood vessels, nerves, hair follicles, and sweat and sebaceous glands. The hypodermis consists largely of adipose tissue.

Skin appendages and specialized structures include hair, nails, sweat glands, and sebaceous glands. The epidermis forms a protective barrier with tight junctions and lipid-rich layers that reduce water loss and entry of microbes.

Developmentally, the skin arises from the ectoderm, with regional thickness differences: thick skin on palms and soles lacks hair, whereas thin skin covers most of the body and typically bears hair and glands. The skin hosts a resident microbiota that contributes to health.

Functionally, the skin provides sensation through cutaneous nerves, participates in immune defense via resident cells, and contributes to vitamin D synthesis under UV exposure. Wound healing proceeds through inflammatory, proliferative, and remodeling phases.

Clinically, skin conditions range from dermatitis and psoriasis to acne and skin cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma. Protective measures include sun protection, infection prevention, and appropriate management of underlying conditions.