Take a close look at your fingernails right now. Most nail changes are harmless, but a handful of specific patterns can be an early sign that something is off in the heart, lungs, liver, kidneys, or blood.
This article draws on U.S. National Institutes of Health guidance and a 2023 systematic review of nail disorders published in Cureus, which cataloged the systemic conditions most often linked to changes in the way nails look and grow.
When fingertips round and bulge
Nail clubbing, where the fingertips widen and the nails curve over them like an upside-down spoon, is one of the oldest bedside clues in medicine. According to the Cleveland Clinic, clubbing "is most often associated with diseases of the heart and lungs, like lung cancer, lung infections, interstitial lung disease, cystic fibrosis or cardiovascular disease."
The Cureus review recorded clubbing in patients with chronic obstructive pulmonary disease, systemic sclerosis, and leprosy, underlining that its causes range from chronic lung damage to autoimmune disease.
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Scooped, spoon-shaped nails
If a nail dips inward deeply enough to hold a drop of water, the medical name is koilonychia. In the Cureus review, every case of spoon-shaped nails traced back to iron-deficiency anemia.
A 2004 clinical review in American Family Physician describes koilonychia as "transverse and longitudinal concavity of the nail, resulting in a 'spoon-shaped' nail," and recommends a blood count and ferritin test to check for low iron.
Red or brown streaks under the nail
Thin splinter-like red or brown lines running lengthwise under a nail are called splinter hemorrhages. Most come from simple trauma. But the American Family Physician review notes they are also "a classic finding in patients with endocarditis", an infection of the inner lining of the heart. The Cureus review linked splinter hemorrhages to ischemic heart disease and high blood pressure as well.
White nails and the liver connection
Nails that turn largely white, with the pink half-moon fading and only a thin dark band remaining near the tip, are known as Terry's nails. The pattern was first described in patients with advanced liver scarring, and has since been reported in kidney failure, heart failure, and diabetes. Isolated white spots after bumping a nail are common and not a concern.
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Yellow, thickened nails
Yellow discoloration is most often ordinary nail fungus. In rare cases, nails that grow slowly, thicken, and take on a yellow hue point to yellow nail syndrome, which the American Family Physician review links to chronic sinusitis, pleural effusions, and internal malignancies.
Dark streaks running the length of the nail
A brown or black band running from cuticle to tip, called longitudinal melanonychia, is often harmless and is especially common in people with darker skin tones. A new, changing, or single-nail dark streak, however, can signal subungual melanoma and warrants a dermatology visit.
When a nail change deserves a doctor's eye
Most nail changes are cosmetic or the aftermath of a bump. A single spot or line that grows out with the nail rarely means trouble. But a nail change that appears suddenly, spreads across several nails, or fails to fade within a few weeks deserves professional evaluation, especially if it comes with fatigue, breathlessness, unexplained weight loss, or a known heart, lung, or liver condition. No nail sign is diagnostic on its own, but it can be the reason to book the appointment.
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