The skin is the largest organ of the body, covering the body's entire surface. It consists of three dependent layers - the epidermis, the dermis and the fat layer. The outermost portion of the epidermis, known as the stratum corneum, is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body. The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels against trauma.

The thickness of the epidermis varies by types of skin as well as by individual and can be especially thin on the face and neck. In addition, as we age, the stratum corneum and remaining layers of the epidermis gradually become thinner and cell rejuvenation (turnover) begins to slow. These changes affect the texture and tone of the skin, causing the skin to loose its ability to retain moisture. Maintaining the integrity and balance of the epidermis is crucial to its functioning as a defender and regulator of the body.

The skin’s next layer, the dermis, is a thick layer of fibrous and elastic tissue (made mostly of collagen, elastin, and fibrillin) that gives the skin its flexibility and strength. The dermis contains nerve endings, sweat and oil glands, hair follicles, and blood vessels.

Fat Layer:
Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area. The fat is contained in living cells, called fat cells, which are held together by fibrous tissue. The fat layer varies in thickness, from a fraction of an inch on the eyelids, to several inches on the abdomen and buttocks in some people.

Skin cell growth follows a natural inside-out growth pattern. Keratinization, which is the maturation and migration of skin cells, begins in the innermost layer of the epidermis and continues outward, ending in the outermost layer of the epidermis. This outer layer is known as the stratum corneum. As new cells are pushed to the surface, the dead cells that constitute the stratum corneum break away and are sloughed off in a process known as desquamation. The processes of cellular regeneration, keratinization and desquamation can take anywhere from 4 to 6 weeks.