The epidermis is a stratified epithelium that forms the outer layer of the skin.

It is composed primarily of keratinocytes and is constantly renewed by the proliferation of stem cells and their progeny that undergo terminal differentiation as they leave the basal layer and migrate to the skin surface.

Basal keratinocytes rest on a basement membrane composed of an extracellular matrix that controls their fate via integrin-mediated focal adhesions and hemidesmosomes which are critical elements of the epidermal barrier and promote its regenerative capabilities.

The distribution of basal cells with optimal activity provides the basement membrane with its characteristic undulating shape; this configuration disappears with age, leading to epidermal weakness.

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