Unhealthy fingernails can show a wide range of visual changes, from discoloration and unusual ridges to changes in shape, texture, or thickness. Some of these are harmless results of everyday bumps and habits, while others signal nutritional problems, infections, or serious internal conditions. Here’s what to look for and what each change typically means.
Color Changes and What They Signal
Healthy nails are a consistent pinkish color with a white crescent at the base. When nails shift to other colors, it often points to something specific happening in your body.
Yellow nails that thicken and seem to stop growing can be a sign of lung disease or rheumatoid arthritis. A serious fungal infection can also turn nails yellow and thick. Smoking and frequent use of dark nail polish are more benign causes, so context matters.
Blue nails indicate your blood isn’t carrying enough oxygen. This can happen with lung conditions or circulation problems. If your nails look persistently blue without an obvious cause like cold temperatures, it’s worth getting checked.
Half pink, half white nails (sometimes called Terry’s nails) can be a marker of kidney disease. The nail bed looks white or pale near the base and pink or brown near the tip, with a sharp line dividing the two zones.
Greenish-black nails usually point to a bacterial infection, often from prolonged moisture exposure. And nails that turn pale or white across their entire surface can reflect anemia or liver problems.
White Spots: Probably Not a Vitamin Deficiency
Small white flecks scattered across your nails are called leukonychia, and they’re commonly blamed on zinc or calcium deficiency. The evidence for that connection is weak. One study of university students found no correlation between white spots and intake of either mineral. In most cases, these marks are simply the result of minor trauma: bumping your nail against something, slamming it in a drawer, or getting too-aggressive manicures. The marks grow out on their own and don’t need treatment.
That said, leukonychia isn’t always harmless. In rare cases involving severe nutritional deficiency (one documented case involved a patient with Crohn’s disease who was deficient in selenium), white changes across the nails resolved after the deficiency was corrected. If white discoloration is dramatic, covers most of the nail, or appears on multiple nails at once, it’s worth investigating further.
Ridges, Lines, and Dents
Vertical ridges running from the base to the tip of your nails are extremely common and almost always harmless. They become more pronounced with age, similar to wrinkles in the skin.
Horizontal lines are a different story. Deep horizontal grooves that run across the nail, called Beau’s lines, form when nail growth is temporarily interrupted. Severe illness, high fever, major surgery, or extreme stress can cause them. Because fingernails grow about 3.5 millimeters per month, you can roughly estimate when the disruption happened by measuring how far the line is from the base of the nail. A groove halfway up the nail formed roughly two to three months ago.
Horizontal white bands (as opposed to indented grooves) can sometimes indicate arsenic poisoning or other toxic exposures, though this is rare.
Pitting
Nail pitting looks like someone pressed the tip of a pin or a small tool into your nail surface, leaving shallow or deep dents. Individual pits range from about 0.4 millimeters (pinpoint-sized) to 2 millimeters across, and you might have just one or two, or more than ten on a single nail. Pitting is strongly associated with psoriasis and can appear before skin symptoms ever show up. It’s also linked to alopecia areata, an autoimmune condition that causes hair loss. In more advanced cases, the nail starts crumbling, loosens, and can even fall off.
Changes in Nail Shape
Clubbing happens when the tips of your fingers swell and the nails curve downward over the fingertip, resembling a small bulb. The angle between the nail and the cuticle becomes rounded rather than forming a sharp crease. Clubbing develops gradually and is linked to conditions that reduce oxygen levels in your blood, including heart problems, chronic lung disease, lung cancer, and lung infections. It’s one of the more medically significant nail changes because it rarely happens without an underlying cause.
Spoon nails (koilonychia) are the opposite of clubbing. Instead of curving down, the nail scoops upward like a tiny spoon. The first sign is usually nails flattening out, followed by a concave dip forming in the center. In advanced cases, the indentation is deep enough to hold a drop of water. Iron deficiency anemia is the most common cause, though it can also occur with thyroid problems or from repeated exposure to certain chemicals.
Dark Streaks and Splinter Hemorrhages
A dark brown or black streak running lengthwise from the base to the tip of a nail is called longitudinal melanonychia. This pigmented band can be completely benign, especially in people with darker skin tones, where it’s a normal variation. But it can also be an early sign of subungual melanoma, a rare but serious skin cancer that grows under the nail.
One key distinction: a bruise under the nail (subungual hematoma) is by far the most common cause of dark nail pigmentation and usually follows obvious or repetitive trauma. Unlike melanoma, a bruise grows out with the nail over several months. Melanoma tends to affect a single nail, and the pigment may spread beyond the nail onto the surrounding skin (known as Hutchinson’s sign). If you notice a new dark streak on one nail with no history of injury, especially one that’s widening or spreading to the skin around the nail, it deserves prompt evaluation.
Splinter hemorrhages look like tiny reddish-brown lines running vertically under the nail, resembling splinters. Most of the time, they result from everyday trauma: sports, housework, or nail-biting account for about 20 percent of cases. But when splinter hemorrhages show up on multiple nails at the same time, appear closer to the base of the nail rather than the tip, or are painful, they can indicate a systemic problem. In particular, they’re a classic finding in endocarditis, a serious infection of the heart valves, especially when accompanied by fever.
Thickened, Crumbly, or Separating Nails
Nails that gradually thicken, become rough or crumbly, and develop a yellowish or brownish discoloration are usually dealing with a fungal infection. This is more common in toenails but affects fingernails too, particularly after prolonged moisture exposure or injury to the nail. Fungal infections don’t resolve on their own and tend to spread to other nails over time, so treatment is worthwhile even if the problem seems cosmetic.
Nails separating from the nail bed (onycholysis) create a white or yellowish gap that starts at the tip and works backward. Psoriasis, fungal infections, thyroid conditions, and reactions to certain nail products can all cause this. The separated portion won’t reattach, but new nail growth behind it will remain connected as the underlying cause is addressed.
How Long Nail Changes Take to Resolve
Fingernails grow at an average rate of about 3.5 millimeters per month. Since a full fingernail is roughly 12 to 15 millimeters long, it takes three to six months for a nail to completely replace itself. That means any mark, ridge, or discoloration caused by a one-time event (illness, injury, nutritional dip) will take several months to fully grow out. If a nail abnormality persists without changing or growing out over that time frame, it’s more likely tied to an ongoing condition rather than a past event.