Piel

Piel, or skin, is the largest organ of the integumentary system in humans and many animals. It acts as a protective barrier between the body and the environment, helps regulate temperature and water loss, and supports sensory perception and immune defense. Skin also participates in the production of vitamin D in response to sunlight and contributes to physical appearance through color and texture.

Anatomically, the skin is organized into three main layers. The epidermis is the outer, waterproof layer made primarily of keratinocytes and includes specialized cells such as melanocytes, Langerhans cells, and Merkel cells. The dermis lies beneath and contains connective tissue, blood vessels, nerves, hair follicles, and glands. The hypodermis, or subcutaneous tissue, sits below the dermis and consists mainly of adipose tissue and loose connective tissue that anchors the skin to deeper structures.

Accessory structures associated with the skin include hair, nails, sweat glands, and sebaceous glands. The dermis houses many sensory receptors and vascular networks that support temperature regulation, touch, and pain perception. The skin also hosts a microbiome that contributes to barrier function and immune defense.

Skin color derives from melanin produced by melanocytes, as well as carotenoids and the optical effects of blood flow. Thickness and elasticity vary by body site, age, and individual characteristics. Wound healing proceeds in stages—inflammation, proliferation, and remodeling—with scarring possible depending on injury depth and context.

Common conditions affect the skin across species, including dermatitis, eczema, psoriasis, acne, and various cancers such as melanoma and non-melanoma skin cancers like basal cell carcinoma and squamous cell carcinoma.