Keratinocytes are cells rich in keratin. The suffix -cyte comes from Latin and means to "combine form" or a "cell". Keratin is the intermediate filament in these cells that provides the toughness needed to withstand environmental insults.

The epidermis, which is the top layer of the skin is a stratified squamous epithelium that consists mainly of keratinocytes, with an admixture of melanocytes, langerhans cells, and merkel cells. Of these, keratinocytes are by far the most numerous, making up the bulk of the epidermis and giving it its characteristic microscopic appearance. The epidermis is typically divided into four layers or strata: stratum basale (SB), stratum spinosum (SS), stratum granulosum (SG), and stratum corneum (SC).

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