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What is dry skin?
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Dry skin, or xerosis (pronounced: zeer-oh-sis), is a common problem for people of all ages, all skin types, and in all climates, but can be worsened by a number of factors. Although not all of these factors can be changed, most dry skin problems can be greatly improved with the proper treatment.
The two factors which are most important in the development of dry skin are the amount of water in the stratum corneum and the amount of oil produced by the sebaceous glands (oil glands) of the skin.
The outer layer of human skin is the epidermis, which is made up of the epithelium and the stratum corneum (SC). The stratum corneum is a layer of flattened, dead skin cells which provides a layer of protection from the elements and from chemicals and infections which are in the outside world. This layer is formed from the epithelium and as new cells are added to the underneath side of the stratum corneum, the out cells peel off, one cell at a time, to keep the layer an even thickness. Although the thickness of the SC is even in a particular body area, the thickness will vary in different regions; for example, the SC of the sole of the foot is much thicker than the thickness of the SC of the forearm. The thickness of the SC varies with age as well. Infants have thin SC which makes their skin feel soft and smooth, but which allows more penetration of irritants or allergens than in an adult. As skin ages the SC is less able to maintain an even thickness and may result in skin feeling rough or looking scaly. This scaly appearance does not necessarily mean that the skin is dry, but a number of the factors which cause drying of the skin may also contribute to an increase in the stratum corneum, causing a similar appearance. A key difference between the two, however, is the presence of itching. Skin that is rough and scaly-looking but not itchy is not dry, and skin that looks normal but is itchy may be xerotic and benefit from treatment for dry skin.
The sebaceous glands secrete oil into the hair follicles and it then flows onto the surface of the skin and prevents the evaporation of water from the SC. The face has the largest oil glands and tends to be much oilier than other areas of the skin. Because of this, having an oily face is not a guarantee that the rest of the skin is oily and protected from xerosis. The amount of oil produced varies by age, as well. Infants produce almost no oil and the production begins to increase in the 10 to 12 year old age group as hormone levels begin rising in early puberty. After about age twenty-five the secretion of oil gradually decreases, becoming lower each year of life.
In an ideal world the production of cells in the SC and the production of oil from the sebaceous glands would be balanced and the level of moisture in the skin would remain constant. Unfortunately, there are many factors in the body and the environment which will change this balanced system and cause the skin to become too dry. Skin that is dry and itchy may develop inflammation and redness, which is called eczema.
Factors which cause skin to become more dry include:
1) Using harsh soaps: These may be either real "soap", such as Ivory, or deodorant or antibacterial soaps such as Zest, etc. Non-soap cleansers, such as Cetaphil or Dove, are gentler.
2) Hard, mineral filled water: A sign of hard water is that soap does not lather much in it. Installing a water softener will remove some of these drying minerals.
3) Bathing or showering in hot water: Hot water removes the natural oil from skin and leaves it vulnerable to drying.
4) Dry climate conditions: These may be seasonal, such as northern winters, or year round, such as in desert climates. Using air conditioning in desert climates also decreases the humidity. Using a "swamp cooler" is often a better choice in very dry conditions; this system blows air over a water source, which then cools by evaporation. This system causes moderate cooling and an increase in humidity, but does not cool as much as traditional air conditioning and can only be used in desert climates, such as those in Colorado and Arizona.
5) Central heating: Heating the dry winter air without adding moisture to it drastically decreases the humidity of the air. Humidifiers can be used to increase the humidity; either attached to or included in the furnace, or free-standing humidifiers in rooms.
6) Using chlorinated swimming pools or hot tubs: The chlorine and bromine used to kill bacteria in pools is both drying and irritating to the skin. The more chlorine or bromine in the water and the hotter the water, the more drying it is.
7) Using alcohol containing products on the skin (this commonly occurs when a patient is itchy and uses alcohol to relieve the itch, thereby causing more dryness and itching). Other alcohol containing products which can be problematic include after-shave products and toners.
Next: Treating dry skin: how to quench your skin's thirst for moisture
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