Where does mitosis (cell division) or replacement of the skin cells take place?

Mitosis, which is the process of cell division, primarily occurs in the stratum basale, also known as the basal layer of the epidermis. This layer is the deepest part of the epidermis, situated just above the dermis. The cells in the stratum basale are basal keratinocytes, which continuously divide to produce new skin cells. As these new cells are formed, they push older cells toward the surface of the skin, where they eventually reach the outermost layer.

The stratum corneum, stratum spinosum, and stratum granulosum do not primarily engage in cell division. The stratum corneum, being the outermost layer, consists of dead keratinized cells that have already completed their life cycle. The stratum spinosum contains living keratinocytes that are more differentiated but are not where the process of mitosis predominantly occurs. The stratum granulosum is involved in the further differentiation of cells that are on their way to becoming part of the outer layer, but it does not play a central role in the actual division of cells.

Thus, the stratum basale is crucial for the renewal of skin cells through the process of mitosis, making it the