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, silks, acrylics and tips.

I am astonished at how some women with elaborately painted daggers extending from their fingertips manage to type, dial cell phones, even sign their names. I wonder what joint deformities may await them decades hence after using their fingers in such unnatural positions.

But many women do not have to wait years to discover untoward consequences of this recent cosmetic rage. They are experiencing allergic reactions to the chemicals in nail products, separation of the nails from their fleshy beds 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 ill-fitting shoes, improper nail hygiene, chronic disease or simply decades of wear and tear and the inevitable changes that accompany aging.

I began painting my toenails this year to avoid looking at the thickened and discolored nails on some of my unadorned toes. The nail bed on one big toe was permanently damaged years ago by an ill-fitting boot, and several other thickened toenails remind me that I have probably walked a million miles in the last 63 years.

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 various procedures involved in current nail cosmetic practices and their possible hazards.

They began with what is often the first step in a manicure: removing the cuticle, sometimes after applying a softener with strong alkalis that break down the keratin in this protective skin. Cuticle removal 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 advised.

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.

Cosmetic nail products are replete with toxic and allergenic chemicals, including toluene, phthalates, camphor and formaldehyde. 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, used to treat brittle nails, 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. The experts point out that "natural nails are often the healthiest choice and need the least maintenance." But they also recognize that getting enthusiasts to abandon nail cosmetics is a lost cause. They suggest these steps:


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


Cuticles should not be removed -- at most, gently trimmed -- and acrylics should be used with great care.


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


Because trimming or 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 of these changes 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.

"Fingernails often become thin and fragile with increasing age; in contrast, toenails often become thicker and harder," the authors noted.

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, trauma or nutritional deficiencies. Both flattening of nails and a concave appearance (spoon nails) are usually normal age-related changes, though spoon nails can sometimes 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 nail problems can be reduced by wearing rubber gloves when washing dishes, wearing 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, caused by damage to the cells of the nail root. 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, affecting nearly half of people over 70, is the fungal infection. These infections can spread person to person or by contact with a contaminated object, like a damp carpet in a locker room, and can cause thickening and disintegration of the nail.

Proper treatment may require identification of the culprit organism because yeasts and molds can be resistant to certain antifungal remedies.

"Topical antifungal creams alone are generally ineffective due to poor nail penetration," the dermatologists noted. And oral therapies can have serious side effects, including rare liver toxicity and drug interactions. Leaving nail fungal infections untreated "is often a wise decision," the doctors concluded.

Jane Brody covers science and biology for The New York Times.