Dry skin is a common problem. most people experience skin dryness, to some extent, from time to time. Dry skin can result either from external causes or from the skin’s inability to retain its moisture.External Causes:

The most important external reasons for dry skin are exposure to dry environments and wind. Artificial indoor heating lowers the relative humidity, which dries out the skin even further.
For that reason, the skin tends to be dryer in the winter. Air-conditioning, with cold, dry air being blown into the room, can cause the skin to become dry as well.
Other external factors that influence the moisture level of the skin are:

washing, and exposure to certain substances.

Washing:

Frequent washing repeatedly removes the oily layer that protects the skin and actually serves to hold in the moisture. Certain types of soaps have a particularly drying effect.