March 2, 2012 Dr. Lawrence Jaeger of New York is an expert in the diagnosis and treatment of skin conditions and is board certified in dermatology and dermatologic surgery. The skin, along with hair and nails, is the protective covering of the body. In addition, the skin prevents germs from entering the body and damaging internal organs. Skin supports the life of all other body parts and plays a role in maintaining the immune system. Skin also helps to regulate body temperature through the sweat glands. When the body becomes overheated, sweat glands give off moisture (perspiration), which cools the body as it evaporates. As the body part responsible for the sense of touch, the skin works with the nervous system to alert the body to potential dangers by detecting pressure, pain, heat, and cold. When exposed to the sun’s ultraviolet rays, the skin manufactures Vitamin D, an essential vitamin for healthy skin. Vitamin D promotes the body’s absorption of calcium, which is essential for the normal development of healthy teeth and bones. Skin is the largest organ of the body. It consists of three layers of tissues: the epidermis, the dermis and the subcutaneous layer. The epidermis is the paper-thin outer layer of the skin. The outer layer of the epidermis consists of dead cells that are always flaking or washing off. These are replaced by new cells manufactured in the lower portion of the epidermis, which move upward to the outside of the skin. As they do so, the cells harden and die. This cycle of cell production and replacement takes about 28 days. The structure of skin The epidermis also contains melanocytes, the cells that contain melanin — the pigment that gives skin its color. Skin color is determined by the amount of melanin in these cells, not cell number. The more melanin, the darker the skin. The dermis, the middle layer of the skin, contains blood vessels, nerves, hair follicles, sweat glands and oil glands. It makes up about 90 percent of the skin’s thickness and is made up of collagen and elastic fibers that give the skin strength and elasticity. The subcutaneous layer, the deepest layer of skin, is mostly composed of fatty tissue. It also contains blood vessels and nerves. The fat insulates the body from extreme heat and cold and provides a cushion to protect the body from injuries.