Corneocytes are terminally differentiated keratinocytes and compose most if not all of the stratum corneum, the outermost part of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers, making them an essential part of the skin barrier property.
Corneocytes are polyhedral, anucleated cells without cytoplasmic organelles, interlocked with each other and organized as vertical columns of 10–30 cells and embedded within a highly hydrophobic lipid matrix to form the stratum corneum. Even if biologically dead they remain active, being filled with keratin, lipids, fatty acids and ceramides.
Corneocytes in the lower part of the stratum corneum are bridged together through specialized junctions (corneodesmosomes). Those junctions disintegrate as corneocytes migrate toward the surface of the skin and result in desquamation. At the same time, as those loosened junctions encounter more hydration, they will expand and connect together, forming potential entry pores for microorganisms across the stratum corneum.
Corneocytes are keratinocytes in their last stage of differentiation. Keratinocytes in the stratum basale of the epidermis will multiply through cell division and migrate toward the skin surface. During that migration keratinocytes will undergo multiple stages of differentiation to finally become corneocytes once they reach the stratum corneum. As corneocytes are continually eliminated through desquamation or through rubbing, skin washing or detergents they are also continually formed through keratinocyte differentiation.
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