If drinking eight glasses of water a day is good for you, will gulping gallons give you
glowing skin like Jennifer Aniston’s? “When you drink water, you’re hydrating your body and helping skin cells function properly,” explains Dr. Patricia Wexler, an A-list dermatologist in Manhattan. She is among those who recommend drinking eight glasses, or two litres, of water a day, noting that any fluids you drink—except those containing alcohol and caffeine—count as internal hydrators. “Your skin will get plumper,” she adds. “It’s really just about optimum function and overall health.” But more is not necessarily better in the hydration game. Wexler cautions that consuming too much water can put you at risk of an electrolyte imbalance, in which low potassium and sodium levels can lead to seizures. (To find your ideal fluid intake, go to nutrition.about.com/library/blwatercalculator.htm.)

When it comes to topical applications, that feeling of instant relief is deceptive. “Bathing and washing are actually dehydrating,” says Wexler, “because water evaporates off your skin and robs it of moisture.” Oftentimes, water is one of the first ingredients in many
skin-care products, yet, according to Wexler, this doesn’t mean that it’s the most important ingredient in the formula. “Water just serves as a base that all the other ingredients— humectants like hyaluronic acid and glycerine—are suspended in or mixed with,” she says. Wexler recommends that those with very dry skin seek out products in which water isn’t necessarily the first ingredient listed and look for glycerine, ceramides, essential fatty acids (EFAs) and hyaluronic acid instead.

Conserving water at the cellular level is the crucial challenge for promoting healthy skin, and it’s one that fascinates Leslie Baumann, a dermatologist based in Miami Beach, Fla. On the skin’s surface, water conservation is achieved with a barrier of cholesterol, ceramides and EFAs— hence, the most effective moisturizers (primarily prescription formulas aimed at eczema and psoriasis sufferers) offer all three.

Maintaining water inside the skin cells is the job of our natural moisturizing factor (NMF), which refers to cells made up of fatty acids. Our NMF allows the skin to sense how much humidity is in the environment and preserve water within the skin cells accordingly. “So, if you’re in humid Miami, you’ll produce less NMF than if you’re in the desert,” says Baumann. Unfortunately, skin-care products can’t help much because, as she notes, nobody has cracked the code on NMF yet, but we do know that foaming soaps and cleansers will strip it from the skin and ultraviolet light will block its production.

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These days, what scientists are most excited by—and what cosmetics chemists are trying to capitalize on—is the 2002 discovery of aquaporin 3, a protein that facilitates the passage of water between skin cells. Baumann describes it as a drinking straw with an open/close valve. “We don’t understand how the cell regulates the aquaporin 3 valve yet, but this hasn’t stopped cosmetics companies from using newly identified botanical ingredients [Ajuga turkestanica, for one] that turn it on, allowing more water to ‘pump’ through it,” says Baumann. “We don’t know if that’s even desirable. How do we know that opening the pore doesn’t just let water drain out or move somewhere else?” So, when it comes to skin care, like good environmental stewardship, conservation is the best practice.

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