Cell division occurs primarily in the stratum basale, the deepest layer of the epidermis.

Here's why:

* Stem cells: The stratum basale contains stem cells that continuously divide to produce new keratinocytes. These cells then migrate upwards through the layers of the epidermis.

* Replacement: As the older keratinocytes move upwards, they differentiate and become filled with keratin, eventually dying and shedding at the surface. This process is called keratinization.

* Continuous renewal: The constant cell division in the stratum basale ensures the skin's continuous renewal and repair.

Let me know if you have any other questions!