Nail discoloration covers a wide spectrum of color changes, from faint white bands to deep black streaks, and the causes range from a stubbed toe to serious internal disease. The color itself often narrows down the possibilities: green usually points to a bacterial infection, a half-white and half-brown nail can flag chronic kidney disease, and a widening dark streak sometimes warrants a biopsy to rule out melanoma. Because the nail plate grows slowly and is mostly transparent, it acts like a biological recording strip, capturing evidence of injuries, infections, medications, and metabolic shifts that happened weeks or months earlier.
What Different Colors Tend to Mean
There is no single cause of nail discoloration, but certain colors cluster around certain categories of problems. White changes can be as benign as small air pockets trapped in the nail plate or as clinically significant as liver cirrhosis. Yellow nails are common with fungal infections and aging but also appear in a rare syndrome linked to lung disease and lymphedema. Brown or black pigmentation raises the most concern because it overlaps with melanoma, yet the vast majority of dark streaks turn out to be harmless melanocyte activation. Green nails almost always implicate one specific bacterium. Blue discoloration of the half-moon area at the nail base has been tied to heavy-metal exposure. Red or reddish-brown patches can reflect psoriasis in the nail bed or tiny hemorrhages running lengthwise under the nail.
A useful first step when you notice a color change is to ask a few questions: How many nails are affected? Did it appear suddenly or gradually? Is there pain or nail separation? A single nail turning dark after you dropped something on your foot is very different from every nail slowly yellowing over several months.
White Nails and Internal Disease
When most or all of the nail bed looks white, doctors sometimes call it leukonychia. The version that matters most medically is called Terry nails (or proximal apparent leukonychia), where the nail appears almost entirely white except for a narrow darker band at the tip. Research has linked this pattern to liver cirrhosis in particular. A study using capillaroscopy found that the presence of this whitening was independently associated with cirrhosis and active alcohol abuse even after adjusting for age and sex, though it disappeared after liver transplantation in many patients.1PubMed Central. Clinical and capillaroscopic findings in patients with liver disease and proximal apparent leukonychia (Terry nails and its variants) The whiteness is thought to result from changes in the tiny blood vessels beneath the nail rather than a change in the nail plate itself.
A related pattern, Lindsay nails (also called half-and-half nails), divides the nail into a white proximal portion and a reddish-brown distal portion with a sharp line between them. This is strongly associated with chronic kidney disease, particularly in patients on dialysis. The distal brown band occupies roughly 20 to 60 percent of the nail length and does not fade when you press on it.2Mayo Clinic Proceedings. Half-and-Half Nails in a Patient With Diabetic Nephropathy The white half appears to result from thickened capillary walls and reduced blood flow, while the brown half comes from melanin deposits driven by hormonal changes related to kidney failure.3PubMed Central. Chronic kidney disease entertained from Lindsay’s nails: A case report and literature review Previous studies have reported this nail change in up to about 40 percent of dialysis patients, and it tends to become more common the longer someone has been on dialysis.4PubMed Central. A prospective study of cutaneous abnormalities in patients with chronic kidney disease
Neither Terry nails nor Lindsay nails cause symptoms on their own, and they are not dangerous in themselves. Their value is as a visual clue. If you notice them on your own nails or a family member’s, they are worth mentioning to a doctor, especially if kidney or liver function has not been checked recently.
Green Nails and Pseudomonas Infection
A nail that turns green, greenish-yellow, or greenish-black is almost always caused by Pseudomonas aeruginosa, a common bacterium that thrives in moist environments. The condition, sometimes called green nail syndrome or chloronychia, typically develops in people whose hands spend a lot of time in water, soap, or detergent. It is especially common in elderly individuals and in nails that already have some separation from the nail bed (onycholysis), which creates a pocket where bacteria can settle.5Europe PMC. Chloronychia: green nail syndrome caused by Pseudomonas aeruginosa in elderly persons The green color comes from pigments the bacteria produce, not from the nail tissue itself dying.
Green nail syndrome is usually painless, though there can be mild swelling around the cuticle. Treatment typically involves an oral antibiotic, and keeping the nail dry is critical for both treatment and prevention. If you work in food service, healthcare, or cleaning and you notice a nail starting to take on a greenish hue, cutting back on prolonged water exposure and seeing a dermatologist early can keep it from spreading.
Dark Streaks and the Melanoma Question
A brown or black longitudinal streak running from the base of the nail to the tip, called longitudinal melanonychia, is one of the most anxiety-provoking nail changes because it overlaps with subungual melanoma, a rare but serious cancer. In practice, the overwhelming majority of these streaks are benign. They result from activation or mild proliferation of the melanocytes (pigment cells) sitting in the nail matrix and are especially common in people with darker skin tones, where they can appear on multiple nails without any underlying disease.
The challenge is sorting the harmless from the dangerous. A retrospective study from Korea found that streaks associated with melanoma tended to be wider, more likely to include multiple colors, and more likely to be accompanied by nail plate distortion compared to benign streaks. When they ran the numbers, a streak wider than about 28 percent of the nail’s total width was the strongest predictor of melanoma under the nail.6PubMed Central. Predictor of Subungual Melanoma against Benign Longitudinal Melanonychia: A Retrospective Cohort Study from Korea Another study found that patients with subungual melanoma presented with wider bands and had carried the streak for a longer time, though interestingly, a standard clinical checklist sometimes used to screen for melanoma did not reliably distinguish benign from malignant cases.7PubMed. Retrospective single-center study evaluating clinical and dermoscopic features of longitudinal melanonychia, ABCDEF criteria, and risk of malignancy
What this means for you: a new, single dark streak that is widening, darkening, or bleeding into the surrounding skin deserves prompt evaluation by a dermatologist. Multiple narrow, stable brown lines across several nails in someone with darker skin are usually a normal finding. If there is any uncertainty, a biopsy of the nail matrix is the definitive test.
Distinguishing Blood from Pigment Under the Nail
A subungual hematoma, the purple-black patch you get after slamming a finger in a door, can look disturbingly similar to melanoma when it first appears. The key clinical difference is history: hematomas follow an injury and grow out with the nail, while melanocytic streaks tend to persist in the same position because they originate from cells in the matrix that keep producing pigment as the nail grows.
Dermoscopy, a technique that uses a magnifying lens and polarized light, helps clinicians tell the two apart. Under the scope, blood typically appears as rounded blobs with wispy edges at the far end, while melanin deposits form more regular bands or lines.8PubMed. Onychoscopy: A practical guide A newer imaging technique, optical coherence tomography, can go even further. In a study comparing hematomas to melanocytic lesions, blood showed up as sharp, sickle-shaped dark areas with bright borders, while the one melanoma case examined displayed irregularly distributed curved blood vessels that looked distinctly different from the clustered red dots seen in benign spots and hematomas.9PubMed. Examination of Subungual Hematomas and Subungual Melanocytic Lesions by Using Optical Coherence Tomography and Dermoscopy
If you have a dark spot under a nail and cannot recall injuring it, or if a presumed hematoma does not grow out within a few months, those are reasons to get it checked.
Psoriasis and Other Skin-Related Nail Changes
Psoriasis does not just affect the skin on your elbows and scalp. Up to half of people with psoriasis eventually develop nail involvement, and the color changes can be distinctive. The classic sign of nail-bed psoriasis is the “oil drop” or “salmon patch,” a translucent yellowish-red spot that shows through the nail plate. The yellow component comes from abnormal skin-cell buildup underneath the nail, and the reddish tones come from the inflamed plaque beneath.10Anais Brasileiros de Dermatologia. Nail psoriasis: a review of the literature These patches can be confirmed with dermoscopy, where they show up as distinct discolored areas corresponding to psoriatic plaques in the distal matrix and nail bed.11PubMed Central. Comparative Study of Clinical and Dermoscopic Features in Nail Psoriasis
Splinter hemorrhages, tiny dark lines that run lengthwise under the nail like splinters, are another form of discoloration worth knowing about. They result from bleeding in the nail bed’s tiny blood vessels and can show up in people who work with their hands a lot. But they also appear in psoriasis, lichen planus, and a range of systemic conditions including infections and vasculitis.12PubMed. Splinter hemorrhages of the nails: a systematic review of clinical features and associated conditions A single splinter hemorrhage on one nail is usually nothing to worry about. Multiple ones across several nails, especially if you have not been doing heavy manual work, deserve a closer look.
Drug-Induced Nail Discoloration
Chemotherapy is one of the most common medication-related causes of nail color change. Many chemotherapy drugs activate the pigment-producing cells in the nail matrix, leading to darkening that can appear as diffuse pigmentation across the entire nail or as distinct longitudinal bands, depending on whether the drug activates melanocytes broadly or in clusters.13PubMed Central. Nail Changes Induced by Chemotherapeutic Agents Several nails are usually affected at once, and the discoloration grows out after treatment ends, though that can take months given how slowly nails grow.
Chemotherapy is far from the only culprit. Antimalarials like hydroxychloroquine can turn nails bluish-grey. Some antibiotics, particularly tetracyclines, are linked to yellowing. Antiretroviral drugs used in HIV treatment can cause longitudinal brown streaks that mimic melanonychia. If you notice nail discoloration after starting a new medication, the timing itself is a strong clue. The change is usually cosmetic and reversible once the drug is stopped, but you should let your prescriber know so they can decide whether it warrants a switch or just monitoring.
Toxins, Heavy Metals, and Blue Lunulae
Some of the more dramatic forms of nail discoloration come from toxic exposures. Arsenic poisoning, for example, can produce transverse white bands across the nails known as Mees’ lines. These horizontal stripes result from heavy-metal deposition in the nail matrix and serve as a visible timeline of exposure, moving outward as the nail grows.14PubMed Central. Arsenic poisoning and Mees’ lines Because nails grow at a known rate, the position of the lines can even help estimate when the poisoning occurred.
Silver is another metal that leaves its mark. Prolonged ingestion of colloidal silver, sometimes taken as an alternative-health supplement, can cause argyria, a permanent blue-grey discoloration of the skin. The lunulae, the pale half-moons at the base of the nail, can turn a striking blue. One case involved a woman who drank colloidal silver mixed into her water over an extended period and developed blue lunulae along with elevated copper levels.15PubMed. Blue lunulae: argyria and hypercopprecaemia Cases like this are rare but serve as a reminder that the nail can act as a window into what is circulating in the bloodstream.
Yellow Nail Syndrome
Yellow nail syndrome deserves its own mention because it is easy to confuse with ordinary yellowing from fungal infection or aging. It is a rare condition defined by a combination of thick, slow-growing, yellow or greenish-yellow nails along with lower-limb swelling and lung problems like chronic cough, bronchiectasis, or fluid around the lungs.16PubMed Central. Yellow nail syndrome: a review Chronic sinusitis often tags along as well.
What makes it tricky to diagnose is that the full set of features is not always present at the same time. A review of 249 patients found that all three hallmarks appeared together only about 27 to 60 percent of the time.17JEM Reports. A rare case of yellow nail syndrome in the emergency room setting: A case report A patient might show up with thick yellow nails and leg swelling but no cough yet, or with nail changes and recurrent sinus infections but no lymphedema. The cause is still not fully understood, though lymphatic dysfunction is the leading theory. If your nails have thickened and turned yellow and you also have unexplained swelling in your legs or recurrent respiratory issues, this is worth raising with a doctor rather than assuming it is just a fungal problem.
Aging, Nutrition, and Everyday Causes
Not every nail color change hides a disease. As people age, nails commonly develop longitudinal ridges and take on a dull, yellowish-grey appearance. Growth slows down, and the plate can become thicker and more opaque.18PubMed Central. Nail changes and nail disorders in the elderly These changes are a normal part of aging and do not require treatment, though they can be cosmetically bothersome.
Nutritional deficiencies occasionally surface through the nails as well. Vitamin B12 deficiency, for instance, has been reported to cause hyperpigmentation that can affect the nails as an early and sometimes sole physical sign.19PubMed Central. Hyperpigmentation as a Primary Symptom of Vitamin B12 Deficiency: A Case Report Iron deficiency can make nails pale, thin, and spoon-shaped. These are relatively easy to test for and, when caught, reversible with supplementation.
Frequent exposure to nail polish, especially darker shades, is another common and completely harmless cause of yellowish staining on fingernails. Acetone-based removers can dry out the nail plate, making it look dull and white at the surface. Giving nails a break from polish for a few weeks usually resolves the discoloration entirely.
How Long It Takes for Nail Discoloration to Grow Out
Once the cause of a nail color change is removed, whether it is a medication, an injury, or an infection that has been treated, the discolored portion of the nail does not simply disappear. It has to grow out. Fingernails grow at an average rate of about 3.5 millimeters per month, while toenails grow at roughly 1.6 millimeters per month.20PubMed. Growth rate of human fingernails and toenails in healthy American young adults That means a fingernail takes roughly four to six months to fully replace itself, and a big toenail can take a year or more.
Growth rate varies by age, season, and which digit is affected. The middle finger tends to grow the fastest, and growth generally slows with age. This is why chemotherapy-related discoloration or Mees’ lines from arsenic exposure can linger long after the cause is gone. Patience is genuinely part of the treatment. If the discoloration is not growing out at all, that is a different signal: it may mean the underlying cause is still active, or that the color change originates from persistent changes in the nail matrix itself rather than something embedded in the plate.
Rare Vascular Causes
Not all nail discoloration comes from pigment, infection, or trauma. In some cases, the color change originates from abnormal blood vessel growth in the nail matrix itself. One documented case involved a woman with brownish pigmentation on the proximal and lateral portions of her fingernails. Histopathological examination revealed that the discoloration came from proliferation of dilated capillaries and small hemorrhages within the nail matrix, which tinted the nail plate from below.21PubMed Central. Proximal and lateral chromonychia with capillary proliferation on the distal nail matrix Cases like this are uncommon, but they illustrate that the same dark brown color can have entirely different mechanisms depending on whether the source is melanin, blood, or something else entirely. When the clinical picture does not fit a standard pattern, a biopsy of the nail matrix remains the most reliable way to reach a definitive answer.