The skin is composed of three layers: the epidermis, the dermis, and the fatty layer. Here, we are primarily concerned with the epidermis, for that is where healing soaps do their work. New skin cells form and rise from the bottom of the epidermis; at the top, old cells slough off. The life cycle of these cells is twenty-eight to thirty days, though the cycle can be hastened by adverse conditions such as sun- or windburn, abrasion, or lack of sleep.