By cell renewal do you mean proliferation or multiplying?

Cell renewal is the replacement of cells by the proliferation of the basal stem cells. 

The skin has multiple layers and the body constantly replenishes cells that naturally work their way up through those layers and eventually fall off. The goal of this endless cell renewal is to replace the epidermis (outer skin layer) which turns over about every one to two months. To have this taking place at the optimum rate means skin looks healthier and younger.

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