There are many good reasons to drink water: It’s refreshing, and it helps your brain function, maintains energy levels, regulates body temperature, aids in digestion, and ultimately keeps your body healthy. (You couldn’t survive more than a few days without a sip.)
 
But “humans aren’t like plants. Our skin doesn’t perk up when we consume water,” says Katie Rodan, a dermatologist in the San Francisco Bay area and a coauthor of Write Your Skin a Prescription for Change. In fact, when you ingest it, “water doesn’t go straight to the skin,” she says. “It goes through the intestines, gets absorbed into your bloodstream, and is filtered by kidneys. Then it hydrates cells.” When it comes to moisturizing skin, drinking water falls short.
 
 

What Does Work

Your skin type, whether it’s dry, oily, or a veritable combo platter, is largely determined by your genes. That natural moisture level then fluctuates depending on what your skin’s protective lipid barrier is exposed to. This lipid layer helps keep moisture in and germs and irritants out. (That’s why dry skin can become red and itchy.)
 
Minimizing your exposure to depleting elements―low humidity, harsh winds, dry heat, high altitude, sun, alcohol, long baths―and avoiding stripping soaps can prevent the loss of natural oils. “Diet can play a role in strengthening your skin’s ability to maintain moisture, too,” says Leslie Baumann, a professor of dermatology at the University of Miami, in Florida. Foods rich in the essential fatty acids found in walnuts, flaxseed, salmon, and olive oil can help skin cells stay hydrated. A study by the Institute of Experimental Dermatology, in Germany, also revealed that women who took flaxseed- or borage-oil supplements (2.2 grams a day) for 12 weeks experienced a significant increase in skin moisture and a reduction in roughness. A healthy diet with three to five servings a week of fatty acids will suffice for the average person, says Baumann. But if you suffer from very dry skin or eczema, consider flaxseed-, evening-primrose–, or borage-oil supplements. All are good sources of alpha or gamma linolenic fatty acids. Take as directed.