The skin is the outermost covering of body tissue. As the largest organ of the body it protects the internal organs from the environment. Its cells are continually being replaced as they are lost by wear and tear. The skin consists of a thin outer layer, the epidermis, and a thicker inner layer of living cells, the dermis. There are a total of 7 layers in the skin, all representing different stages of skin cell development.
The outermost part of the epidermis is composed of dead cells, which form a tough, horny, protective coating. As these dead cells are worn away, they are replaced by new cells which are produced by rapidly dividing living cells in the innermost part of the epidermis. Between the outer and inner parts is a transitional region that consists of both living and dead cells. Most of the cells in the epidermis are specialized to produce keratin, a hard protein substance that is the main constituent of the tough, outermost part of the epidermis. Some of the cells produce the protective pigment, melanin, which determines skin color and a corresponding ability to resist UV damage.
The dermis is composed of connective tissue interspersed with various specialized structures, such as hair follicles, sweat glands, and sebaceous glands that produce an oily substance called sebum. The dermis also contains blood vessels, lymph vessels, and nerves. The life cycle of skin cells is about 28 days and extends to 45 days by the time we are 60.
The most common skin disorders are eczema, psoriasis, seborrhea, and rosacea. Dry skin is only a conditional response to our surrounding environment and is not generally considered a true skin disorder unless caused by an identified disease.
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