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The outermost layer of skin; a self-renewing, waterproof barrier built from keratinocytes that protects against the environment.
Medically reviewed & updated
The epidermis is the thin, avascular outer layer of skin you actually see and touch. Although it is the most superficial layer, it does the heavy lifting of barrier protection, keeping water in and microbes, chemicals, and ultraviolet (UV) radiation out. It is made mostly of keratinocytes, which are continuously produced at the base and pushed upward as they mature and flatten.
The epidermis is organized into four or five distinct layers, from deepest to most superficial: the stratum basale, stratum spinosum, stratum granulosum, the stratum lucidum (present only in thick skin of the palms and soles), and the stratum corneum. The stratum basale houses the stem cells that constantly regenerate keratinocytes. As cells migrate upward they accumulate keratin and lipids, then die and lose their nuclei. The outermost stratum corneum is a sheet of flattened, dead, keratin-filled cells called corneocytes that form the body's first physical line of defense and limit water loss.
Besides keratinocytes, the epidermis contains three specialized cell types. Melanocytes (in the stratum basale) make the pigment melanin, which absorbs UV light and shields DNA. Langerhans cells are immune sentinels that detect and present foreign antigens. Merkel cells act as light-touch mechanoreceptors. Together these give the epidermis its three core jobs: physical barrier, immune surveillance, and pigmentation. The entire epidermis turns over roughly every month, which is why it heals scrapes so efficiently.
Because the epidermis is the body's outer shell, it is central to many common conditions. A defective barrier underlies the dryness and inflammation of eczema (atopic dermatitis), while accelerated keratinocyte turnover produces the thick, scaly plaques of psoriasis. Melanocytes can give rise to melanoma, the most dangerous skin cancer, while basal and squamous keratinocytes give rise to the more common non-melanoma skin cancers, largely driven by cumulative UV damage. Burns are also classified partly by how deeply they penetrate the epidermis. This information is educational and not a substitute for professional medical advice.