Nail Care and the Changes Worth Checking

Nails are made of keratin, the same protein as hair, and they grow slowly: about 3 millimeters a month for fingernails and about half that for toenails. A fingernail takes around six months to replace itself completely and a big toenail up to 18 months, which is why changes in the nail can reflect events from months earlier.

Everyday care

• Leave cuticles alone. The cuticle seals the gap between nail and skin. Cutting or pushing it back hard opens a route for bacteria and fungi and is a common cause of paronychia, a painful infection around the nail. Moisturizing is enough.
• Cut straight across, then smooth the corners. Rounding toenails too deeply is a leading cause of ingrown nails.
• Use a file in one direction rather than sawing back and forth, which can split thin nails.
• Wear gloves for washing up and cleaning. Repeated wetting and drying is one of the main causes of brittle, peeling nails.
• Moisturize nails and hands after washing, especially in winter.

Why nails become brittle

Brittle nails that split, peel or break easily are very common, especially after age 50 and in women. The main causes are repeated wetting and drying, harsh cleaning products, frequent nail polish remover and cold, dry air. Less often, brittle nails are linked to thyroid problems or iron deficiency. Keeping nails a little shorter, filing rough edges promptly so they don't catch, and applying a moisturizer or a product containing urea or lactic acid can make a noticeable difference within a few months.

Polish, gels and UV lamps

Regular polish is harmless for most people, though frequent acetone removers dry the nail. Gel and dip manicures last longer but are harder on nails because removal often involves soaking and scraping. Gel polish is hardened under UV lamps, and a 2023 laboratory study published in Nature Communications found that exposure to these lamps damaged DNA in human cells. The real-world cancer risk is not known and is likely low for occasional use, but dermatologists suggest applying sunscreen to the hands or wearing fingerless gloves during the curing step.

Do supplements help?

Biotin is the supplement most often marketed for nails. A few small studies found it helped people with brittle nails, but there is little evidence it does anything for people who aren't deficient, and deficiency is rare. High-dose biotin can also interfere with some blood tests, including tests for thyroid function and heart attacks. The FDA has warned about this, so tell your doctor if you take it.

Treating nail fungus

Fungal nail infections are stubborn because the fungus lives under and within the nail. Over-the-counter creams rarely reach it. Prescription options include oral antifungals such as terbinafine, usually taken for about 6 weeks for fingernails and 12 weeks for toenails, and medicated nail solutions that are applied daily for many months. Even after successful treatment, the nail looks abnormal until it grows out, which can take a year or more for a big toe. Keeping feet dry, wearing sandals in shared showers and not sharing nail clippers reduce the chance of reinfection.

Nail care with diabetes or poor circulation

People with diabetes or circulation problems should take extra care with toenails, since a small cut or ingrown nail can turn into a serious infection when sensation or healing is reduced. Health organizations recommend checking feet daily, cutting nails straight across, and seeing a podiatrist for thick nails, ingrown nails or any wound that isn't healing. Salon pedicures that involve cutting cuticles or shaving calluses are best avoided.

When a nail change is worth a doctor's visit

• A new dark stripe running the length of the nail, especially on one nail only, can rarely be a sign of melanoma.
• Spoon-shaped nails that curve upward can be associated with iron deficiency.
• Horizontal grooves (Beau's lines) can appear a few months after a serious illness, high fever or chemotherapy.
• Thick, yellow, crumbly nails often mean a fungal infection, which affects up to about 10 percent of people and usually needs prescription treatment.
• Nail separating from the nail bed without an obvious injury.