Dry skin occurs when the moisture, or water, content of the skin is decreased for any reason.
The surface of the skin holds a certain amount of water. When the water content decreases, the skin becomes dry, itchy, and uncomfortable.
Some individuals have a genetic predisposition to dry skin. As people age, their skin tends to become drier. Dry air, resulting from winter's low humidity and the use of indoor heat, can cause skin to dry out. Long, hot baths and showers can also make skin dry.