Britannica Sources used in this answer

How does the epidermis protect vertebrates from chemicals, radiation, and microbes?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

The epidermis serves as a vital protective barrier for vertebrates, utilizing both physical and immunological mechanisms to defend against external threats.1

Physical Protection

The epidermis is composed of closely packed cells that form a mechanical barrier against chemicals, radiation, and microbes. Its outermost portion, the stratum corneum, consists of dead, flattened cells filled with keratin, a tough, insoluble protein. In mammals, this barrier is reinforced by lipid-rich platelets packed between cornified cells, which prevent the inward passage of chemicals. Additionally, skin glands secrete substances such as fatty acids and the enzyme lysozyme, which can neutralize or destroy certain bacteria.1234

Immunological Defense

Beyond its physical structure, the epidermis acts as an active component of the immune system. Langerhans cells function as "sentinel" cells that detect foreign particulate substances and alert the lymphoid system to initiate a defensive response. Furthermore, keratinocytes secrete epidermal cytokines, which enhance immune responsiveness and assist the body in reacting to infections or injuries.5