Cause: Cold, arid air sucks the moisture out of hands and nails, according to Jin Soon Choi, owner of New York City's Natural Hand and Foot Spas. Dishwashing liquid is also super-harsh and drying, Choi says.

Fix: Doug Schoon, nail expert and scientist for CND, says hydrating the entire the nail plate is key. He explains that (carefully) removing white, flaky bits of cuticle (dead skin on the nail plate) with sharp nippers is okay, but warns against cutting or aggressively pushing back the skin at the nail base (called the eponychium). "This is living tissue that prevents bacteria from getting into the skin, and you can cause an infection by removing it," he says. "Just keep it moisturized and gently push it back, and in about a month it'll be smoother and less overgrown." Prevention is the best medicine, and gloves are your new best friend, whether they're rubber (for dishes) or woolly (for warmth). Always slather on moisturizing products and drink plenty of water to keep hydrated from the inside out, Choi says. "You don't need pricey stuff. I love Sally Hansen Maximum Growth Cuticle Pen, $5.49 because it's easy to carry and use." Nails need moisture too, so rub it in and follow with Sally Hansen Shea Butter Hand and Body Butter,$6.95.

Photo: Courtesy of hooked-on-nails.com

Cause: Constantly applying and removing nail polish will cause nails to look dry, according to Schoon. And frequent hand washing can also contribute to nail peeling.

Fix: "If you keep doing new manicures, you'll end up removing the natural oils that maintain moisture in the skin and nail plate," Schoon says. Instead of switching hues every other day, keep the color you have. He also recommends adding a few drops of oil to your nail polish remover to counter its drying effects, and he suggests rubbing even more nail oil onto the nails after removing polish. To solve the water damage issue, wear rubber gloves when washing dishes and keep hands/nails constantly moisturized with a rich cream. Try Kiehl's Unusually Rich-But Not Greasy At All-Hand Cream With SPF 10, $15.50).

Photo: Courtesy of hooked-on-nails.com

Cause: Dark or intense colors are more to blame here, Schoon says, so be aware of which polish you choose. Also, the nicotine in cigarettes can leave a yellow tinge.

Fix: "Some less expensive brands use dyes instead of pricier pigments in their polishes, which can seep into nails and stain them just like an Easter egg," Schoon says. So when it comes to deep tones like black, blue or plum, it's worth it to splurge. To attack the discoloration, Schoon suggests using a whitening product that's formulated especially for nails, like Orly Nail Whitener, $7.50, and most importantly, applying a protective layer of thick base coat, like Essie Protein Base Coat, $8, to help ward off future yellowing. And of course, quit smoking (but you already knew that).

Photo: "Nail Structure & Product Chemistry", Second Edition Doug Schoon M.S., Thomson/Delmar Learning

Cause: A fungal infection, which almost always occurs on the feet, can make nails become rough, crumbly, thickened and yellow or cloudy in appearance. A bacterial infection can appear between the nail and the nail bed or between a natural nail and an artificial nail -- it will also discolor the nail. Both infections should be treated immediately.

Fix: Your doctor or derm can prescribe medicine to treat nail fungus. Schoon warns against at-home remedies, explaining that professional help is the only way to take care of the situation. He says that frequenting sanitary salons and keeping your home tools hygienic is the most efficient prevention. Wear flip-flops at the gym and pool to prevent picking up an infection, wash and dry feet thoroughly after exercise to stave off fungus (which thrives in dampness) and avoid wearing the same shoes day after day. Surprisingly, it's bacteria, not fungus, that almost always causes nail infections on the hands, especially underneath acrylic nails. Improper cleaning before applying them is the culprit, so be vigilant; ask your doc if they need to be taken off. "After having them removed, gently buff off the infected areas, then start treatment," says Los Angeles-based celebrity manicure pro Carla Kay. "For the following two months, apply Duri Rejuvacote, $12, and Duri Miracote, $7, which strengthen nails to bring them back to health."

Photo: "Nail Structure & Product Chemistry", Second Edition Doug Schoon M.S., Thomson/Delmar Learning

Cause: Schoon says the appearance of white spots and ridges are caused by trauma or genes, not missing nutrients in your daily diet.

Fix: Damaging the nail matrix will cause it to produce irregular cells, which manifest as soft, white spots as the nail grows out. Schoon says the only way to prevent them is to protect the hands and try to avoid future damage. You can cover up white spots with opaque shades of polish, but be sure not to buff them, since these areas tend to be soft and weak. When it comes to ridges, heredity or age are the culprits -- if Mom or Grandma have them, chances are you will, too. Most of us will develop them as we age; it's normal. Schoon says grooves that run vertically from the nail plate to the tips are simply areas that grow thinner, and warns that aggressive treatment can make the entire nail thin and weak. Instead, even them out with ridge filler or gently buff them. Skyy Hadley, owner of the As "U" Wish Nail Spa in Hoboken, N.J., says to dab on some CND SolarOil, $11 -- which is really rich -- then use a gentle buffer to smooth the nail surface.

Photo: "Nail Structure & Product Chemistry", Second Edition Doug Schoon M.S., Thomson/Delmar Learning