Читать книгу Good Skin - Ingrid Wood - Страница 8

Your skin’s front line of defence is the epidermis. It allows light to partially pass through it as it would through frosted glass, and is nourished by blood vessels in the deeper layers of the skin that provide it with oxygen and ‘skin food’. Plump, moist skin cells are developed in the basal layer of the epidermis. As each new layer of skin cells form, the cells move up towards the skin’s surface, becoming flattened as they do so. By the time they reach the outer horny layer of the skin – known as the stratum corneum – they are effectively dead. These layers of densely packed cells, known as corneocytes, are filled with a protein called keratin, and a fatty lipid. Like the tiles of a roof, they overlap in layers to form a strong, protective shield that prevents water loss. Throughout your life, the cells of the surface layer are continually being worn away and replaced with new cells from below. In normal skin, it takes about 30 days for the cells to move up to the surface. If the outer layer is being lost quickly – due to sunburn, for example – these cells will be replaced more swiftly.

LAYERS OF THE SKIN

Below the stratum corneum are the Langerhans cells, which patrol for invaders, and the melanocytes – cells that produce the pigment melanin which helps determine the colour of your hair and skin. Melanocytes evolved to help the skin ward off dangerous UV radiation; the melanin on the skin surface absorbs UV light, protecting the cells below. Within the melanocyte, melanin is packaged in small membrane sacs called the melanosomes. The difference in pigmen tation of various ethnic groups is due to the way in which the pigment is packed in these melanosomes. Skin cells in black-skinned people do not contain more melanocyte cells, but the melanin granules are larger and individually dispersed. Black-skinned people, therefore, are genetically programmed to be more resistant to UV damage because of the profusion of melanin within their cells. People with white skin tend to suffer more from unprotected sun exposure because they have less melanin, and because their melanosomes are smaller and grouped together in membrane-bound clumps. Skin cells in Asian people contain smaller melan osome complexes that are more densely packed than those found in Caucasian skin cells.