Epidermise

Epidermise is a term sometimes used in non-English contexts to refer to the epidermis, the outermost layer of the skin in humans and other vertebrates. It forms a protective barrier against mechanical injury, pathogens, and water loss.

The epidermis is a stratified squamous epithelium composed of four or five sublayers. In thick skin (palms and soles) the layers are basale, spinosum, granulosum, lucidum, and corneum; in thin skin the lucidum is absent. The dominant cell type is keratinocytes, which originate in the basal layer and migrate outward, while melanocytes, Langerhans cells, and Merkel cells are interspersed among them.

Protected by the stratum corneum, the outermost keratinocyte layer provides most barrier function and minimizes water loss. The epidermis is avascular and relies on diffusion from the underlying dermis for nutrients. Melanocytes produce pigment that influences skin color and UV protection; Langerhans cells contribute to immune defense; Merkel cells are involved in light touch sensation.

Developmentally, the epidermis derives from ectoderm. Keratinocyte turnover from the basal layer to the surface takes about 28 days in young adults. The epidermis interacts with the dermis and, though hair follicles and glands reside mainly in the dermis, epidermal cells extend into the surface to form appendages.

Clinically, epidermal characteristics vary with age, sun exposure, and genetics, influencing aging and cancer risk. Common disorders include psoriasis, eczema, and dermatitis, which reflect epidermal dysfunction or immune involvement. Treatments often aim to restore barrier function and regulate epidermal renewal.