Epidermis
Definition
The epidermis is the outermost layer of the skin and serves as the body's primary physical barrier against the environment. It is composed of multiple sublayers, with the stratum corneum at the very top and the basal layer at the bottom, where new skin cells (keratinocytes) are produced. As keratinocytes migrate upward through the epidermis over approximately 28 days, they flatten, harden, and eventually die, forming the protective stratum corneum. The epidermis also contains melanocytes (which produce melanin for pigmentation and UV protection), Langerhans cells (immune cells), and Merkel cells (for touch sensation). The epidermis contains no blood vessels — it receives nutrients by diffusion from the dermis below. Most topical skincare products primarily act on or within the epidermis.
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