The epidermis is made up of 2 cell types known as Keratinocytes. Keratinocytes are protein cells which make up the majority of the epidermis and are arranged in layers above the (base) basal layer.

New keratinocytes are made by a division of keratinocytes in the basal layer of the epidermis. As new keratinocytes are made, the keratinocytes in the layers above the basal layer are pushed upwards towards the surface of the skin. As the keratinocytes are pushed upwards, they begin to flatten and die. By the time they reach the stratum corneum, the outermost layer of the epidermis, they are ready to exfoliate as dead skin cells.

This process of skin renewal occurs continuously in the skin and takes around 30-40 days to complete. Via this inbuilt renewal process, the skin is able to ensure its protective barrier remains in optimum condition through its lifetime. This barrier is so vital for the body's health that we will die if we lose more than 50% of our epidermis. The advent of artificial skin has revolutionized the treatment of burns victims by providing an artificial skin barrier to protect burns victims until they can re-establish their own skin barrier function.

We can degrade the effectiveness of the epidermal barrier through excessive UV exposure and excessive use of skin cleansing agents. In normal healthy skin, the number of new cells made in the basal layer is equal to the number of dead skin cells exfoliating from the skin's surface.