What Is It?
Normal skin has a soft, supple texture because of its water content. For skin to feel soft, pliable and "normal," its top layer must contain a minimum of 10% water — and ideally between 20% and 35%. To help protect the outer layer of skin from losing water, the skin's sebaceous glands produce an oily substance called sebum. Sebum is a complex mixture of fatty acids, sugars, waxes and other natural chemicals that form a protective barrier against water evaporation. If the skin doesn't have enough sebum, it loses water and feels dry. If environmental factors cause more water evaporation and overwhelm the ability of sebum to prevent water loss, the skin will shrivel and crack.
Dry skin, also called xerosis, is a very common problem in modern societies, affecting people of all ages, even infants. In the United States, most cases of dry skin are related to one or more of the following factors: