That white mark or mysterious dent may hint at other things going on in your body. Here are some points to consider.

By Hannah Morrill
Updated April 02, 2014
Red cross made out of fingernails
Credit: Mitchell Feinberg

Doctors get really excited when they talk about nails. That’s because, like the rings of a tree, the bumps, dents, and ridges on them reveal a lot about your well-being. “Nails provide an amazing time line of a patient’s habits and health history,” says Dana Stern, a dermatologist in New York City. Below are a few of the most common nail markings, their meanings, and what to do about them. Treat your nails now for better health overall—and a prettier manicure down the road.

What You See: White Spots

These imperfections on an otherwise healthy nail signal damage to the cuticle, the thin but durable skin that borders the lower nail plate (which is the hard, translucent part of the nail). The cuticle acts as a seal, keeping in moisture and blocking out bacteria and drying chemicals (like formaldehyde-infused polishes and acetone-based polish removers). When cuticles are trimmed too aggressively, or if you have a habit of pushing, cutting, or picking them, irritants can slip below the surface, compromising the nail-growth process. The result: white accumulations, called punctate leukonychia, within the nail plate.

The solution: These spots can’t be scraped off. Your best bet? “Leave your cuticles alone,” says Chris Guest Adigun, a clinical assistant professor of dermatology at the New York University School of Medicine, in New York City. Also stick to acetone-free polish removers and formaldehyde-free polishes. In a few months, the cuticles will heal, allowing healthy nails to grow out.

What You See: A Deep Groove

This horizontal mark, called a Beau’s line, emerges after a single traumatic event. The more intense the circumstances, the more severe the dent. Illness, fever, pregnancy, and even stress, such as grieving, can cause one. “Cells halt metabolic activity and stop producing smooth, uniform nails,” says Adigun. Two to three months later, the imperfect product of these dysfunctional cells is visible in the form of a groove.

The solution: A Beau’s line takes up to six months to grow out. You can make the dent less noticeable with a ridge-filling base coat that smooths and resurfaces, like Essie Ridge Filling Base Coat ($8.50, Do not try to file or buff the line away, as this will only weaken the nail.

What You See: Horizontal Depressions

These dings usually happen when you’ve done something directly harmful to the nail matrix (the half-moon at the base of the nail), such as (ouch) shutting a drawer on your finger. However, a series of dips along the center is often a telltale sign that you’ve been repetitively picking at or pushing back the cuticle. “Most people aren’t even aware of the tic,” says Stern.

The solution: The depressions will grow out. Quitting the picking habit will prevent future grooves from forming.

What You See: Split Nail Tips

If your nails break easily, the culprit is probably overexposure to water and chemicals, both of which weaken nails.

The solution: Get the daily recommended intake of 30 micrograms of biotin, which helps to strengthen nails. (It’s available in many foods, like fish and eggs, or as a supplement.) A few adjustments to day-to-day habits can help, too. Pull on a pair of cotton-lined rubber gloves to do the dishes. Also avoid dehydrating alcohol-based hand sanitizers; instead, wash with soap and apply hand cream afterward for the extra moisture. During manicures, use a non-acetone polish remover and a strengthening base coat.

What You See: Rough White Patches

If parts of the nail plate look white and appear roughed up, they are probably keratin granulations that were caused by wearing polish for too long or using drying polish remover too often (say, more than three times a week). The chemicals in these products cause the nail plate to dry out and the keratin molecules within it to clump together into what looks like a chalky stain.

The solution: A one-month holiday from nail polish and polish remover will clear up the nail plate nicely. To prevent a reappearance, go bare for a few days between manicures.

What You See: Smooth Longitudinal Ridges

For people over 30, these ridges are normal, and they grow more pronounced with age. (Think wrinkles, but for nails.) But if the lines emerge suddenly, you may have onychorrhexis, a symptom of a range of inflammatory skin conditions, like psoriasis, alopecia (hair loss), and lichen planus (an itchy rash on the body).

The solution: See a dermatologist to treat the skin condition and, by extension, your nails systemically. To even out the appearance of your nails in the meantime, gently buff with a 240-grit file, says New York City manicurist Gina Viviano. But for thin, weak nails, leave the marks alone, or cover them up with a ridge-filling, nail-strengthening base coat before polishing.

What You See: A Thick, Yellow Toenail

If the patches cover most of the nail, you may have a fungal infection called onychomycosis, often caused by athlete’s foot contracted by going barefoot in damp public places.

The solution: Fortunately, this common condition, affecting about 10 percent of the population, is treatable with a dermatologist-prescribed topical or oral medication. The infection disappears in 12 to 18 months. Avoid a recurrence by wearing shower slippers in locker rooms and near pools.