Nail discoloration usually signals something minor, like a bruise growing out or a reaction to nail polish, but the specific color matters. Yellow, white, green, blue, brown, and black nails each point to different causes ranging from fungal infections and nutritional deficiencies to circulation problems and, rarely, skin cancer. Understanding what each color means helps you figure out whether your nails just need time or whether something deeper is going on.
Yellow Nails
Yellow is the most common discoloration people notice, and fungal infection is the most frequent culprit. Fungi thrive in warm, moist environments, so toenails are hit more often than fingernails. The yellowing usually starts at the tip or edge of the nail and gradually spreads inward. The nail may also thicken, become brittle, or develop a slightly crumbly texture.
Psoriasis can also turn nails yellow, sometimes accompanied by tiny pits or dents in the nail surface. Heavy use of dark nail polish without a base coat leaves behind yellow staining too, though this is purely cosmetic and grows out on its own.
A rarer cause is yellow nail syndrome, where all or most nails turn yellow, thicken, and seem to stop growing. About 8 in 10 people with this condition also have lymphedema, a type of fluid buildup and swelling in the soft tissues. Researchers believe problems with the circulatory or lymphatic system trigger the changes. Yellow nail syndrome has been reported at higher rates in people with autoimmune diseases, thyroid disease, rheumatoid arthritis, and certain cancers. There’s also a possible link to titanium exposure from joint replacements, dental implants, or certain medications.
White Spots and White Nails
Small white spots, each about 1 to 3 millimeters across, are extremely common and almost always caused by minor trauma to the base of the nail. Bumping your finger against something or aggressive manicuring can damage the cells as the nail forms, leaving behind a white mark that slowly grows out. These spots are harmless and need no treatment.
White lines running across the nail have a wider range of causes. Repeated trauma is still the most common explanation, especially in women who get frequent manicures or in people whose toenails regularly press against the front of their shoes. In rare cases, transverse white lines appearing across multiple nails at the same time can signal heavy metal exposure (historically arsenic or thallium), chemotherapy effects, or systemic infections.
When most of the nail turns white, the picture changes. Terry’s nails describes a pattern where nearly the entire nail looks white or frosted, with only a thin pink or brown strip remaining at the tip. The normal half-moon shape near the cuticle disappears. In the 1950s, a physician named Richard Terry found that more than 8 out of 10 people with severe liver cirrhosis had this nail pattern. A related pattern called Lindsay’s nails, where the lower half is white and the upper half is brown or pink, is associated with kidney disease. Both of these warrant a medical workup.
One quick way to tell the difference between a problem in the nail itself and a problem in the nail bed underneath: press on the nail. If the white color disappears under pressure, the issue is in the nail bed. If it stays white, the discoloration is baked into the nail plate itself.
Green Nails
A greenish or blue-green tint on a nail almost always points to a bacterial infection caused by Pseudomonas aeruginosa. This bacterium produces a pigmented biofilm that coats the nail surface, giving it that distinctive color. It’s more likely to take hold when the nail is already compromised by a fungal infection, chronic inflammation around the cuticle, or separation of the nail from the nail bed.
Green nail syndrome is especially common in people whose hands are frequently wet: dishwashers, bakers, barbers, janitors, healthcare workers, and homemakers. Exposure to water and chemicals softens the nail and creates entry points for bacteria. Artificial nails and nail enhancements may also increase risk by trapping moisture between the natural nail and the overlay. Without treatment, the infection tends to worsen rather than resolve on its own.
Blue or Purple Nails
Blue-tinged nails typically reflect low oxygen levels in your blood. Oxygen-rich blood is bright red, but when oxygen drops, blood turns darker with a bluish tone that shows through the nail bed. This is called cyanosis.
Cold temperatures are the most common and least worrying trigger. When you’re exposed to cold, blood vessels in your hands and feet constrict to preserve core body temperature, temporarily reducing blood flow and giving nails a bluish cast. Caffeine and nicotine can cause similar vessel narrowing.
Persistent blue nails that don’t resolve with warming, however, can signal heart or lung conditions that reduce oxygen circulation. If the blue color appears only in your hands and feet (peripheral cyanosis) rather than also affecting your lips and face, the problem is more likely related to circulation than to overall oxygen levels. Either way, nails that stay blue deserve attention.
Vitamin B12 deficiency is another, less obvious cause. B12-related nail changes can present as a bluish discoloration, blue-black pigmentation, or dark longitudinal streaks running the length of the nail.
Brown and Black Streaks
A brown or black line running lengthwise down a nail is called longitudinal melanonychia. In many cases, this is completely benign, caused by increased activity of the pigment-producing cells in the nail matrix. It’s more common in people with darker skin tones. In African Americans, Asians, and Native Americans, some degree of nail pigmentation is a normal finding.
The concern is subungual melanoma, a type of skin cancer that can appear as a dark streak under the nail. Dermatologists use an ABCDEF framework to evaluate these streaks. The features that raise suspicion include: being in your 50s to 70s, a brown-to-black band wider than 3 millimeters with irregular borders, a streak that changes over time, involvement of the thumb or big toe (the most commonly affected digits), pigment that extends beyond the nail onto the surrounding skin fold (known as Hutchinson’s sign), and a personal or family history of melanoma. A new or changing dark streak on any nail warrants a dermatology visit. Diagnosis requires a biopsy.
Medications That Change Nail Color
Certain drugs can activate the pigment-producing cells in the nail matrix, causing the nail to develop brown-to-black longitudinal bands or become uniformly darkened. Chemotherapy drugs are the most well-known offenders, particularly cyclophosphamide, hydroxyurea, fluorouracil, and anthracycline-class drugs like doxorubicin. The discoloration typically appears weeks into treatment and grows out after the medication is stopped.
Some medications can also cause the nail to separate from the nail bed, especially antibiotics in the quinolone class, which may trigger a light-sensitivity reaction. When the nail lifts, tiny hemorrhages can form underneath, adding reddish-brown spots to the picture. Even topical preparations applied directly to nails can cause staining. These medication-related changes are almost always temporary, but they can be alarming if you’re not expecting them.
Nutritional Deficiencies
Iron deficiency is one of the clearest nutritional causes of nail changes. As iron stores drop, nails can become pale, brittle, and eventually spoon-shaped, curving upward at the edges and dipping in the center like a shallow bowl. This shape change, called koilonychia, is a well-established sign that your body isn’t getting enough iron.
B12 deficiency produces a different pattern. Rather than shape changes, B12 depletion tends to cause color changes: bluish nails, dark streaks, or a reticulate (net-like) darkened pattern. These changes can appear even before other classic B12 deficiency symptoms like fatigue or numbness become obvious, making your nails an early visual clue.
How Long Discoloration Takes to Grow Out
If the cause of your discoloration has been addressed or was a one-time event, the stained portion of nail simply needs to grow out and be trimmed away. Fingernails grow at an average rate of about 3.5 millimeters per month, meaning a full fingernail takes roughly four to six months to replace itself. Toenails grow at about 1.6 millimeters per month, so a full toenail can take 12 to 18 months to completely turn over. This is why a bruised toenail or a fungal infection that’s been treated can look discolored for what feels like an unreasonably long time.
Colors That Need a Dermatologist
Not every discolored nail needs medical attention, but certain patterns shouldn’t be ignored. A new or changing dark streak on a single nail is the most urgent, because it could indicate melanoma. Nails that lift away from the nail bed, with or without color changes, often signal an infection that won’t clear without treatment. Greenish-black discoloration from a bacterial infection tends to worsen on its own. Pitting that looks like tiny icepick marks can be a sign of psoriasis or another systemic condition. And if your nails start to curve downward and your fingertips seem to bulge, that type of change (called clubbing) can point to lung, heart, or liver disease.
Yellow nails that thicken and stop growing, nails that turn mostly white, or spoon-shaped nails that develop without an obvious cause are all worth having evaluated, since they can reflect conditions elsewhere in your body that you might not feel yet.