Dry skin is a problem that affects many people in varying degrees. Some people occasionally have mildly tight or flaky skin that goes away quickly with treatment. But other people have flaking and itching that bothers them constantly causing daily and nightly distress.
Most of the factors below cause dry skin by affecting the stratum corneum, the top layer of the epidermis. The stratum corneum works like plastic wrap around the body, keeping harmful substances and germs out while keeping water and oils in the skin making it supple and pliable.
Older age is one of the most common causes of dry skin. Most people start getting dry skin in their 50's. By their 60's everyone has some degree of dry skin. As we age the epidermis becomes thinner and the stratum corneum can't hold as much water as it used to.
Climate changes outdoors and indoors are a major cause of dry skin. Low humidity occurs in certain areas of the United States year-round and in most areas in the winter. Low humidity also occurs inside with certain types of heaters and air conditioners. Cold winds can also cause dry skin.
Exposure of the skin to direct sunlight is a cause of dry skin in any climate. The heat of the sun dries out the skin by reducing the natural oils in the skin. This can lead to flaky skin with premature wrinkles.
You would think that water would be good for dry skin, not cause it, but water can dry the skin out in many ways. The problem with water is it takes the skin's natural oils with it when it evaporates. The more frequently the skin comes in contact with water and the hotter the water, the more oils get leeched out of the skin leaving it dry and tight.
Soaps and Detergents
Soaps and detergents cause dry skin in the same way water does. They surround the water molecules in the skin and take them away when they get rinsed off the skin. Certain soaps are more likely to dry the skin out. A good rule of thumb is any bar soap is going to be more harsh on the skin than a liquid soap. Some liquid body cleansers actually help moisturize the skin.
Certain medications cause dry skin by reducing the water content of the stratum corneum or making it more porous and leaky. Some common medications that can cause dry skin are diuretics like hydrochlorothiazide or furosemide, retin-a, cholesterol medicines like pravastatin and simvastatin, and accutane.
Certain diseases cause dry skin for different reasons. Dry, flaky skin is the hallmark for two common skin diseases, atopic dermatitis and psoriasis. Malnutrition, kidney disease, and dialysis can all cause dry skin because these conditions can deprive the skin of needed vitamins and other building blocks.
Misery, L. “How the skin reacts to environmental factors.” Journal of the European Academy of Dermatology and Venereology. 21 Suppl 2(2007): 5-8.
Pons-Guiraud, A. “Dry skin in dermatology: a complex physiopathology.” Journal of the European Academy of Dermatology and Venereology. 21 Suppl 2(2007): 1-4.