Your nails are a visible record of what’s been happening inside your body over the past several months. Because fingernails grow at an average rate of about 3.5 millimeters per month, a mark halfway up your nail reflects something that happened roughly two to three months ago. Changes in color, shape, texture, or thickness can point to nutritional gaps, organ problems, infections, or simply minor trauma you’ve already forgotten about. Here’s what to look for and what it actually means.
White Spots and White Nails
Small white spots scattered across a nail are extremely common and almost always caused by minor bumps or pressure on the nail matrix (the tissue under your cuticle where the nail forms). They grow out on their own and aren’t a sign of calcium deficiency, despite the popular myth.
When whiteness covers most or all of the nail, the story changes. Terry’s nails describes a pattern where the nail plate turns a frosted, ground-glass white and the pale half-moon at the base disappears entirely. About 80% of people with severe liver disease, particularly cirrhosis, have this pattern. Muehrcke’s lines are a different presentation: paired white horizontal bands that run across the nail. They appear when blood protein levels drop significantly, which can happen with kidney disease, liver disease, or malnutrition. One quick way to tell Muehrcke’s lines from other markings is to press on the nail. The lines temporarily disappear under pressure because they’re in the nail bed, not the nail itself.
Yellow, Brown, and Green Discoloration
Nails that gradually turn yellow are most often dealing with a fungal infection. The nail thickens, becomes brittle, and may take on a yellow, brown, or even greenish tint as the infection progresses. Fungal infections are slow and stubborn, and they won’t resolve without treatment.
A rarer cause is yellow nail syndrome, a condition involving the lymphatic system. It produces a distinctive triad: thickened yellow nails that grow very slowly, swelling in the legs or ankles from fluid buildup, and respiratory problems like chronic bronchitis, recurrent sinus infections, or fluid collecting around the lungs. If your nails have turned yellow and you’re also dealing with unexplained swelling or breathing issues, that combination is worth investigating.
Brown discoloration at the tip of the nail, covering roughly the outer half while the base stays white, is known as half-and-half nails. In chronic kidney disease, increased pigment production darkens the far end of the nail bed. This pattern is distinct enough that it sometimes helps clinicians spot kidney problems before other symptoms become obvious.
Ridges and Grooves
Vertical ridges running from the base of the nail to the tip are, for most people, simply a sign of aging. They become more pronounced over time and are rarely a concern.
Horizontal grooves are a different matter. Called Beau’s lines, these are actual depressions or dents that run side to side across the nail. They form when nail growth temporarily slows or stops due to a significant stress on the body: a high fever, a serious illness, surgery, chemotherapy, or a period of severe nutritional deficiency. Because you can measure how far the line has grown from the cuticle, you can estimate roughly when the disruption happened. A groove sitting about 7 millimeters from the base, for example, would correspond to an event about two months prior.
Pitting and Crumbling
Tiny dents or pits scattered across the nail surface are a hallmark of psoriasis. These pits can be shallow or deep and often appear on multiple nails at once. In some people, nail pitting shows up before any skin plaques develop, making it an early clue.
Fungal infections can look superficially similar because they also cause nail damage, but the pattern is different. Fungal nails tend to thicken and crumble at the edges, often starting at the tip and working backward. The discoloration is usually uneven, and debris may collect under the nail. Psoriasis pitting, by contrast, creates distinct small holes in an otherwise intact nail surface. It’s possible to have both conditions at the same time, which complicates things, but the distinction matters because treatments are completely different.
Spoon-Shaped Nails
Nails that flatten out and eventually curve inward, forming a shallow scoop that could hold a drop of water, are called spoon nails. This change typically develops gradually. You may first notice your nails looking unusually flat before the concave shape becomes obvious.
The most common cause is iron deficiency anemia. When your body’s iron stores drop low enough, nail tissue loses its structural integrity. Spoon nails in a child under age two can be normal and temporary, but in adults they almost always warrant a blood test to check iron levels. Less common causes include thyroid disorders and prolonged exposure to petroleum-based chemicals.
Clubbing: When Nails Curve Downward
Clubbing is the opposite of spooning. The fingertips enlarge and the nails curve over them, wrapping downward like the round side of a drumstick. It develops gradually over weeks or months. The underlying cause is an overgrowth of soft tissue at the fingertip, driven by growth factors released in response to low oxygen levels or chronic inflammation.
You can check for early clubbing with a simple test: place two matching fingernails back to back, nail to nail. Normally, a small diamond-shaped gap appears between the nail beds. If that gap is missing and the nails press flat against each other, clubbing may be present. Conditions linked to clubbing include lung disease, heart disease, inflammatory bowel disease, celiac disease, and cirrhosis. It’s one of the nail changes that most reliably points to something significant happening internally.
Splinter Hemorrhages
These are thin, dark lines that run vertically under the nail, following the direction of nail growth. They’re typically 1 to 3 millimeters long and start out reddish-purple before darkening to brown or black within a few days. They look exactly like a tiny splinter got lodged under the nail.
A single splinter hemorrhage on one nail is almost always from minor trauma, even if you don’t remember it. The red flag is when they appear on multiple nails at once without an obvious injury. That pattern can be associated with endocarditis, an infection of the heart valves, or with other conditions affecting blood vessels. Multiple unexplained splinter hemorrhages, especially alongside fever, fatigue, or joint pain, are worth getting checked out promptly.
Brittle, Peeling, and Splitting Nails
Nails that peel in layers, split at the tips, or break constantly are one of the most common complaints, and the cause is usually environmental. Repeated cycles of wetting and drying, frequent hand washing, exposure to cleaning products, and acetone-based nail polish removers all strip moisture and oils from the nail plate.
Nutritional causes are less common but real. Biotin deficiency can weaken nails, and supplementation has shown benefits in some studies. Thyroid disorders, both overactive and underactive, can also make nails thin and fragile. If brittle nails don’t improve after a few months of protecting them from chemical exposure and moisture cycling, a blood workup can help rule out underlying causes.
Dark Streaks and Lines
A dark brown or black streak running lengthwise from the cuticle to the tip of a single nail deserves attention. In people with darker skin tones, pigmented bands across multiple nails are common and benign. But a new, solitary dark streak that widens over time, becomes irregular in color, or bleeds pigment into the surrounding skin can indicate subungual melanoma, a form of skin cancer that develops under the nail. This is uncommon but serious, and early detection makes a significant difference in outcomes. Any new, isolated dark streak that changes over weeks or months should be evaluated.