Dry air may contribute to skin dryness, air conditioned environment is usually blamed. Hand skin is dry by frequent exposure to water such as in cleaning ladies or canteen workers (doing the dishes). Water washes away natural protective oily cover of the skin. Similarly, people with excessive adherence to hygiene who wash their hands too frequently also have problems with dry skin.
Untreated diabetes leads to elevation of blood sugar level (hyperglycemia). Sugar leaks into urine and takes with minerals and water. Dehydration and dry skin is therefore typical for hyperglycemic state. On the contrary, hypoglycemic state is accompanied with moist sweaty skin.
Some drugs undoubtedly cause skin dryness. Diuretic agents are great example. These drugs increase water losses in kidneys and are great in heart failure management. Overdose with diuretics may, however, cause severe dehydration with dry skin. Retinoids are other causative factor of dry skin. These preparations are used in treatment of acne and dryness of skin and lips is really common side-effect.