You don't have to look far - at the hands (and feet) of women in all walks of life, at the displays in every pharmacy, at the nail salons that have proliferated around the country - to realize that nails are in.

There are more than 50,000 nail salons in the United States, and women (with the help of some men) spend more than $6 billion a year on nail care and cosmetics, from base coats and polish to wraps and tips.

I am astonished at how some women with elaborate daggers on their fingertips manage to type, dial cell phones, even sign their names. I wonder what deformities may await them after years of using their fingers in such unnatural positions.

But many women do not have to wait years to discover consequences. They are experiencing allergic reactions to the chemicals in nail products, separation of the nails from flesh, and a variety of other problems.

Other women are discovering a different set of nail problems involving both fingers and toes, an eventual result of wearing ill-fitting shoes, improper nail hygiene, chronic disease or simply decades of wear and tear and the inevitable changes of aging.

In the September issue of Women's Health in Primary Care, two New York dermatologists, Dr. Herbert P. Goodheart of Mount Sinai Hospital and Dr. Hendrik Uyttendaele of Columbia University Medical Center, reviewed the procedures involved in current nail cosmetic practices and their hazards.

They began with cuticle removal, which should be discouraged because it can lead to inflammation and infections of the surrounding tissue and nail root and cause permanent nail deformities, the doctors said.

They also warned against the use of a wooden pick under the nails when getting a "French manicure," which can contribute to fungal infections and loss of the nail.

Many of these components can cause allergic reactions, and not just involving the nails. For example, eyelid dermatitis can result when someone touches or rubs her eyes with polished nails, transferring the toluene-sulfonamide-formaldehyde resin in the polish to highly sensitive skin.

Nail hardeners with fiber are another source of allergic reactions, as is the acrylic glue used to attach many nail wraps and tips and the plastic artificial nails used to elongate natural nails. In addition, minor pressure exerted on the tips of artificial nails can damage the underlying natural nails and cause partial or complete nail loss.

To reduce the risk of infection, women who get professional manicures should buy their own manicure instruments that they bring to the nail salon.

Women should periodically refrain from using nail polish to promote overall nail health and to permit occasional inspection of the natural nail for abnormalities.

Because filing natural nails into an "egg-shape" to make the fingers look longer increases the risk of separation from the nail bed, a grooming method similar to that used for toenails - flat tips with long corners - is more sensible and less likely to result in broken nails.

In three earlier issues of the journal, Goodheart and Uyttendaele described the various degenerative changes that affect nails as people age. While most are normal and benign and require no treatment, some predispose the nails to infections and deformities and others are signs of underlying disease that should be diagnosed and treated.

One of the most common effects of age on nails is the appearance of longitudinal ridges, a normal development that is not a sign of disease. Both flattening of nails and a concave appearance (spoon nails) are usually age-related changes, though spoon nails sometimes can be a sign of iron deficiency anemia, diabetes, thyroid disease or vitamin deficiencies.

Nails often become more brittle with age. Contributing factors include frequent use of nail products, overexposure to detergents or water or, possibly, iron deficiency, thyroid disease or a decrease in peripheral circulation.

Brittle nails can be helped by wearing rubber gloves when washing dishes, wearing warm gloves in cold weather, applying moisturizing creams at bedtime and after washing, keeping nails short, using a soft file and taking a vitamin supplement containing B-complex.

The nails of older people often become dull, opaque and discolored, possibly a result of a fungal infection under the nail. Yellow nails may be a sign of respiratory tract diseases. White nails may indicate liver or kidney disease, lupus, gout, cardiac insufficiency or poisoning, or they may be a side effect of certain drugs.

Among the most distressing nail deformities in older people are pincer nails - painful pinched tips of the toenails - which may be caused by ill-fitting shoes or inflammatory osteoarthritis. They can result in infections and ingrown toenails and often require corrective surgery.

Another distressing toenail problem results from uneven thickening of the nail plate, typically on the big toe. The nail becomes hooked or clawlike, turns opaque and brown, and may require removal of the nail root to stop the damaged cells from producing a new deformed nail.

Perhaps the most common problem that comes with aging is the fungal infection. These infections can spread person to person or by contact with a contaminated object and can cause thickening and disintegration of the nail.

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