Too much soapy water, exposure to harsh chemicals, the normal aging process and certain types of skin diseases are some of the causes of decreased amounts of protective skin oils which in turn causes dry skin.
The mainstay of management is liberal use of moisturizers after washing with luke warm water. Soap should be used minimally. Moisturizers should be reapplied liberally during the day.You can also use a topical cortisone (steroid) cream or ointment like dermacort(hydrocortisone). Adding a humidifier to the central heating system of your home or using a humidifier also helps.
If still the symptoms persisit then possibility of eczema or atopic dermatitis,psoriasis, ichthyosis (fish scale-like skin) or pitted keratolysis is there.Pls consult a dermatologist for clinical examination in that case as treatment is specific for each one. Hope it helps. Take care and pls do keep me posted if you have any additional queries.