What causes dry skin problems?

The stratum corneum acts as an outer 'hide' that can resist injury and help to conserve water in the skin.

    Throughout a person's life, from birth to death, the cells of this layer are continually being worn away and replaced from below with new cells. The wearing process is called desquamation, and the flattened scales of dead skin are called squames (see page 9). Each squame is only about a micrometre thick but some 35 micrometres across. Desquamation tends to slow down as we grow older. In any particular part of the body, however, the results of the processes of cell loss and replacement are that the skin tends to remain the same overall thickness.
    In normal skin, it takes about 30 days for a cell produced by the basal layer to move through the epidermis to the surface. The rate of movement is partly controlled by the rate at which the outer layer is being lost. When stratum corneum cells are being lost quickly -perhaps after sunburn - they are replaced more quickly from below. In skin that has been injured (grazed, for instance) the process speeds up dramatically. Artificially removing the outer layers by the cosmetic process of peeling (exfoliation) also tends to speed up replacement.

The stratum corneum is a very important layer from the point of view of understanding skin, skin problems, skin care and the beneficial effects of cosmetics such as skin moisturizers. It is the part of the skin that forms the junction of the body with the outside world, and it is directly affected by the outside environment, by harsh soaps, by skin care products and by the sun.

It plays a key role in helping to contain moisture within the rest of the skin, and in regulating the natural moisture flow out from the deeper layers to be lost eventually by evaporation from the skin surface. This flow is known as transepidermal water loss (TEWL), and it is important to understand the factors that influence it. Without adequate retained moisture, skin can become dry and unhealthy.
    Under normal conditions up to 15% of the stratum corneum consists of water. This water is vital to enable the stratum corneum itself to work. The natural functions of the skin do not work as well when the stratum corneum contains less than 10% of water, and it becomes dry.

    In the epidermis the spaces between the cells are packed with fats, or lipids, made by the body. One very important group of these lipids is the ceramides, which are also ingredients of some skin care products.

Removal of lipids leads the stratum corneum to break down.