skin

The first line of defence against disease and physical damage, the skin is a complex organ containing different types of tissue.

The surface layer consists of dead, keratin-containing cells which swell in response to moisture and are shed daily. Given time, this layer thickens and hardens in response to friction. If friction is excessive, burns, blisters, and corns can develop. One aim of training is to harden the skin gradually so that it can withstand the forces experienced during activity. This is particularly important in martial arts which use parts of the body to inflict blows.

Beneath the outer layer, lie the living cells of the epidermis, protecting the body from injury and invasion from parasites. This layer also helps to prevent dehydration. Epidermal cells are continually dividing to replace dead cells lost from the surface. Since these cells have such a short lifespan, signs of nutritional deficiency develop quickly and skin condition is a good reflection of inner health. Clear, moist, glowing skin usually indicates that a person is healthy and well nourished.

The middle layer of the skin, the dermis or corium, contains cells with a black pigment, melanin. Melanin shields the underlying layers from the potentially damaging effects of ultraviolet radiation. Also in the dermis, sensory receptors and nerves inform the body of changes in body temperature. They enable a person to respond, sometimes defensively, to pressure, touch, and pain. The dermis is well supplied with blood vessel and sweat glands. These, combined with the action of erectile hairs, form part of the temperature-regulating system in the body. Sebaceous glands associated with the hair secrete oils which keep the skin moist and contribute to waterproofing. The dermis is the region in which wrinkles originate.

The deepest layer in the skin is the subcutaneous layer containing the stores of fat which many people spend much effort and time trying to reduce.

A well-balanced diet with plenty of fluid intake, regular aerobic exercise, and moderate exposure to sunlight can help to maintain a healthy skin. Nutrient deficiencies may cause dryness, roughness, wrinkling, and slow healing of wounds. Particularly important dietary components are the essential fatty acids and vitamins, particularly A, C, E, niacin, and riboflavin, but in developed countries deficiencies of these nutrients are very rare. See also chafing; eczema; and sun-protection factor.