Why Do Tans Fade?
Skin takes a lot of wear and tear, so it naturally regenerates itself. Every 35-45 days the outer layer of the skin, the epidermis, is completely replaced. Since skin pigment is found in this upper layer, any natural or added pigment will be sloughed away in about one month's time. This is why natural tans fade and why many self-tanning products recommend you re-apply the product every few days to maintain your tan.