The stratum corneum is a layer covered with a thin film of water and fat; together, they form the barrier responsible for protecting the skin from bacterial infection and maintaining skin moisture; any damage to this barrier may cause the skin to dry out.
Both external and internal factors can contribute to dry skin. External factors are the principle in this case, and this includes exposure to wind, hot air, dry air, and in the case of low and high temperatures, and exposure to ultraviolet rays.
Also, personal habits may play a crucial role in this context, including, for example, the heavy use of strong detergents, the use of certain drugs, psychological stress, insufficient fluid intake and a special diet. Moreover, internal factors such as hormonal influences, diseases, or ageing can contribute to dry skin.