Causes of Dry skin

Though most cases of dry skin (xerosis) have an environmental cause,
certain diseases also can significantly affect your skin.
Potential causes of dry skin include:

- Weather. In general, your skin is driest in winter, when
temperatures and humidity levels plummet. But the reverse may be true
if you live in desert regions, where temperatures can soar, but
humidity levels remain low.
- Heat. Central heating, wood-burning stoves, space heaters and
fireplaces all reduce humidity and dry your skin.
- Hot baths and showers. Taking long, hot showers or baths can dry
your skin. So can frequent swimming, particularly in heavily
chlorinated pools.
- Harsh soaps and detergents. Many popular soaps and detergents strip
moisture from your skin. Deodorant and antibacterial soaps are usually
the most damaging.
Many shampoos may dry your scalp.
- Sun exposure. Sun dries your skin, and its ultraviolet (UV)
radiation penetrates far beyond the top layer of skin. The most
significant damage occurs deeper, leading to deep wrinkles and loose,
sagging skin.
Other skin conditions. People with skin
conditions like atopic dermatitis (eczema) or a skin condition marked
by a rapid buildup of rough, dry, dead skin cells that form thick
scales (psoriasis) are prone to dry skin.
Source: Mayoclinic