Epidermis

The thin, tough outer layer of the skin — the body’s true surface.

Structure

Stacked layers of epithelial cells. New cells form at the base and are pushed upward, flattening and filling with the protein keratin as they go, until the dead outer cells are shed. Thick skin (palms, soles) has five named layers; thin skin has four.

Key cell types

• Keratinocytes — the bulk of the layer; make keratin.
• Melanocytes — make melanin, the pigment that colors skin and absorbs UV.
• Langerhans cells — immune sentinels.
• Merkel cells — involved in touch sensing.

What it does

• Barrier and waterproofing — the outer dead layer seals the body.
• UV protection — melanin shields deeper tissue.
• Renewal — fully replaces itself roughly every month.

Key idea

The visible skin surface is entirely dead cells; the living epidermis works underneath, constantly replacing what wears away.