Discolored nails can signal anything from a minor fungal infection to an underlying health condition affecting your liver, lungs, or heart. The color itself is often the first clue: yellow, white, green, blue, brown, or black each point toward different causes. Most nail discoloration is harmless or easily treatable, but certain patterns warrant a closer look.
Yellow Nails
Yellow nails are one of the most common color changes, and fungal infection is the most frequent culprit. Toenail fungus (onychomycosis) affects roughly 4% of the general population, but among people who already notice something off about their nails, about 17% turn out to have a confirmed fungal infection. The nails typically thicken, become brittle, and take on a dull yellow or brownish-yellow tone that starts at the tip and creeps toward the base.
Beyond fungus, yellow nails can result from frequent use of dark nail polish without a base coat, heavy smoking (nicotine staining), or aging. Certain medications are also known to turn nails yellow, including some cancer chemotherapy drugs, antimalarials, and tetracycline antibiotics.
In rare cases, persistently yellow, thickened, slow-growing nails point to yellow nail syndrome, a condition diagnosed when at least two of three features are present: the characteristic yellow nails, swelling in the legs from fluid buildup (lymphedema), and respiratory problems such as chronic cough or fluid around the lungs. Yellow nail syndrome has also been linked to autoimmune diseases and immune deficiency disorders.
White Spots, Lines, and Patches
Small white spots scattered across a nail are the most innocent form of discoloration. Called punctate leukonychia, they’re almost always caused by minor trauma to the nail matrix, the tissue at the base where your nail grows. Bumping your finger on a counter or aggressive manicuring is enough. These spots grow out on their own and don’t need treatment.
White changes that span the entire nail or form distinct bands are more clinically significant. Terry’s nails, where most of the nail plate turns a pale, opaque white with a ground-glass appearance, were originally linked to liver cirrhosis but have since been found in up to 25% of hospitalized patients regardless of diagnosis. The whiteness comes from reduced blood flow and increased connective tissue in the nail bed.
Muehrcke’s lines are pairs of white horizontal bands running across the nail, separated by strips of normal pink color. They differ from other white markings in one key way: they disappear when you press down on the nail, because the color change is in the nail bed rather than the nail itself. These lines typically reflect low levels of a blood protein called albumin, most commonly caused by kidney disease (especially nephrotic syndrome), liver disease, or malnutrition. Levels below 2.2 grams per deciliter are most often associated with the finding.
Green Nails
A green or greenish-yellow nail almost always points to a bacterial infection caused by Pseudomonas aeruginosa, a common environmental bacterium that thrives in moist conditions. The green color comes from pyocyanin, a pigment the bacteria produce as they colonize the space between the nail and the nail bed. People who work with their hands in water frequently, wear tight shoes that cause the nail to lift, have diabetes, or already have a pre-existing nail condition like fungal infection are most at risk. The discoloration is often painless, which means it can go unnoticed for weeks.
Blue or Purple Nails
Blue or purple nail beds usually indicate that your blood isn’t carrying enough oxygen, a sign called cyanosis. This happens when oxygen saturation drops to roughly 80% or below (normal is 95% to 100%), though detection varies quite a bit. In one study, a quarter of observers failed to identify definite cyanosis even at oxygen saturations as low as 71 to 75%. In people with darker skin tones, an additional 3 to 6% drop in oxygen saturation may be needed before the color change becomes visible.
Chronic lung conditions like COPD, heart failure, and circulatory problems are common causes. Cold temperatures can also trigger temporary blue discoloration by constricting blood vessels in the fingers and toes, which is especially common in Raynaud’s phenomenon. Some medications, including certain heart drugs and silver-containing compounds, can cause a persistent blue-gray tint as well.
Brown or Black Streaks
A dark brown or black longitudinal streak running from the base of the nail to the tip is called longitudinal melanonychia. In people with darker skin tones, these streaks are extremely common and usually benign, resulting from increased melanin production in the nail matrix. Multiple streaks across several nails are generally not a concern.
A single new streak, however, deserves attention because it can occasionally represent subungual melanoma, a type of skin cancer that develops under the nail. Dermatologists use an ABCDEF framework to evaluate suspicious streaks: age (typically 40 to 70) and higher risk in African American, Asian, or Native American individuals; brown-black color with a width of 3 mm or more or a blurred border; change in the band over time; the digit most commonly affected (thumb, big toe, or dominant hand); extension of pigment onto the skin surrounding the nail; and family or personal history of melanoma. A streak that is widening, darkening, or bleeding into the surrounding skin fold is the most important warning sign.
Red Lines Under the Nail
Thin reddish-brown lines running vertically under the nail are called splinter hemorrhages because they look like tiny splinters trapped beneath the surface. They’re caused by damage to the small blood vessels in the nail bed. A single line near the tip of the nail is usually from everyday trauma and is nothing to worry about.
Multiple splinter hemorrhages, especially closer to the base of the nail, can be a sign of more serious conditions. Infection of the heart valves (endocarditis) is the most well-known association. Inflammation of blood vessels (vasculitis) and tiny blood clots that damage capillaries can also produce them. If you notice several of these lines appearing across multiple nails without an obvious injury, it’s worth having them evaluated.
Medications That Change Nail Color
A number of prescription drugs are well documented to alter nail pigmentation. Cancer chemotherapy agents are among the most common offenders, often producing horizontal dark bands, diffuse darkening, or blue-black discoloration across multiple nails. Antimalarials can cause a similar blue-gray hue. Tetracycline antibiotics may turn nails yellow, while the antiviral drug zidovudine frequently causes brown or blue longitudinal streaks. Retinoids and psoralens (used in skin conditions like psoriasis) are also known contributors. Arsenic exposure produces characteristic white horizontal lines that have forensic significance. In most cases, medication-related discoloration is reversible once the drug is discontinued, though it takes time for the affected portion to grow out.
How Long Discoloration Takes to Clear
Because nail discoloration is often embedded in the nail plate itself, it won’t simply “fade.” It has to physically grow out. Fingernails take about 4 to 6 months to fully regrow, while toenails are much slower, averaging 12 to 18 months. After trauma or medical nail removal, toenail regrowth can take up to two years. If you’re treating a fungal infection or have stopped a medication that caused discoloration, expect to see healthy, normally colored nail emerging from the base gradually, pushing the discolored section toward the tip over the course of many months.
Conditions that affect the nail bed rather than the nail plate, like Muehrcke’s lines or cyanosis, can resolve more quickly because the color change disappears once the underlying issue is addressed. Terry’s nails from liver disease, for instance, may improve if liver function improves, without waiting for full nail regrowth.