epidermal

Epidermal is an adjective used in biology to describe anything pertaining to the epidermis, the outer protective tissue in organisms. In animals the epidermis is the outer skin layer; in plants it is the protective outer cell layer covering shoots, roots, and leaves.

In animals, the epidermis is a stratified squamous epithelium whose main cell type is keratinocytes, supported by melanocytes, Langerhans cells, and Merkel cells. It is organized into layers: basale, spinosum, granulosum, lucidum (only in thick skin), and corneum. It serves as a barrier against injury, infection, and water loss, and participates in immune defense and UV protection. Hair, nails, sweat glands, and sebaceous glands all originate from epidermal tissue.

In plants, the epidermis is usually a single cell layer covering all aerial and underground organs. It often secretes a waxy cuticle to reduce water loss. Guard cells form stomata for gas exchange; epidermal cells may produce trichomes (hairs) and root hairs that aid in protection and absorption. In many woody plants, the epidermis is replaced by the periderm (bark) as tissues grow.

Clinical and practical notes: Changes in epidermal structure or function are central to conditions such as burns, psoriasis, and epidermolysis bullosa in humans. In botany, epidermal traits influence transpiration, photosynthesis efficiency, and pest resistance.