The skin is constantly generating new skin cells at its lower layer, the dermis, and sending them to the surface, the epidermis. As the cells rise to the surface they gradually die. Over time, cells start to accumulate unevenly which can give it a dry, rough and dull appearance.
Exfoliation is beneficial because it removes those cells that are clinging on, revealing the fresher, younger skin cells below. This attachment also removes dirt, makeup, and sebum more effectively than a manual cleanse can do, and is better able to cleanse within the uneven surfaces of the skin. It has a purifying action on the skin and reveals a fresher skin complexion.