As we age, our skin gets worse at retaining moisture. After our teenage years, we make less of the molecules that trap water in our skin. Almost every layer of the epidermis gets more barren: We make less natural moisturizing factors, less ceramides and less hyaluronic acid. By age 50 to 70, spots of dry skin show up on even the healthiest of hands, says Dr. Kent Aftergut, a clinical assistant professor of dermatology at the University of Texas, Southwestern at Dallas.
We can't stop our genes from making less moisture-trapping equipment in our skin as we age. But we can stop disabling the equipment we have. For instance, instead of lathering soaps, which yank fats out of our skin, we can switch to mild soaps that don't lather. We also can use creams that replace natural moisturizing factors that our genes have slacked off in making. Urea is one of those factors. But be careful: Some creams promise to replace waning moisturizing factors that the skin can't actually absorb [source: Bonté].
Age isn't the only genetic source of dry skin. Some people have chronically dry skin, starting when they are young. They may have a type of eczema, which stems from a genetic mutation related to one of the elements that holds water in the skin.
Just as for the elderly, part of the solution for eczema can be to replace the missing element in the skin. Scan the labels of moisturizing creams prescribed to people with eczema, and you'll often see ceramides and other fats that people with eczema don't naturally make [source: Aftergut]. The solution doesn't usually stop there, however. Because other bodily systems, such as the immune system, can contribute to the skin condition, patients may need other medications that deal with the broader issue.