Your fingernails can reveal a surprising amount about what’s happening inside your body. Changes in color, shape, texture, and growth patterns sometimes reflect nutritional deficiencies, organ problems, infections, or autoimmune conditions. Most nail changes are harmless, but a few warrant attention. Here’s what to look for and what it actually means.
Vertical Ridges Are Almost Always Normal
If you’ve noticed faint lines running from your cuticle to the tip of your nail, you can relax. Vertical nail ridges are one of the most common nail changes, and they’re a normal part of aging. They develop because the rate of cell turnover in your nail matrix slows over time, and they tend to become more prominent as you get older. These ridges don’t signal any underlying disease.
Horizontal ridges are a different story. Known as Beau’s lines, these are indentations that run across the nail like grooves, and they typically appear a few weeks or months after your body experienced significant stress. Common triggers include high fevers, pneumonia, heart attacks, severe infections like COVID-19 or strep, and even intense emotional stress such as a death in the family or job loss. Chronic conditions that reduce blood flow to the nail, including diabetes, hypothyroidism, and peripheral artery disease, can also cause them. Even a zinc deficiency or inadequate protein intake is enough. Because nails grow slowly, Beau’s lines are essentially a timestamp of when your body went through something disruptive.
Nail Color Changes and What They Signal
The color of your nails, particularly the nail bed underneath, can reflect what’s happening in your liver, kidneys, or lymphatic system.
Terry’s nails appear when most of the nail looks white or frosted, with only a thin brown or pink strip at the tip. The normal half-moon shape near the cuticle disappears. This pattern is most closely associated with liver disease.
Lindsay’s nails (sometimes called half-and-half nails) look white on the half closest to the cuticle and brown or reddish on the other half. This pattern is linked to kidney disease, which can cause nitrogen waste products to build up in the blood and damage nail tissue.
Yellow nails that grow unusually slowly, thicken, or start detaching from the nail bed can point to yellow nail syndrome, a rare condition involving the nails, lungs, and limbs. About 8 in 10 people with this syndrome develop fluid buildup and swelling in their limbs due to poor lymphatic drainage, and many also have chronic coughs or fluid accumulation around the lungs. The nails turn yellow because fluid collecting in soft tissues disrupts normal nail growth.
Spoon-Shaped Nails and Iron Deficiency
Koilonychia, or spoon nails, is one of the more visually distinctive nail changes. The nail softens, flattens, and eventually develops a concave dip deep enough to hold a drop of water. It usually develops gradually rather than appearing overnight.
The most common cause is iron deficiency anemia. Vitamin B deficiencies can also contribute. People who eat a vegetarian diet have a higher risk because plant-based iron is harder for the body to absorb. If your nails are curving inward, it’s worth having your iron levels checked, since correcting the deficiency typically allows the nails to grow back normally over several months.
Pitting and Autoimmune Conditions
Small, pinpoint depressions scattered across the nail surface are called pitting, and they’re a hallmark of two autoimmune conditions: psoriasis and alopecia areata (an autoimmune form of hair loss).
The two conditions affect nails differently. In alopecia areata, pitting is the most common nail sign, reported in about 30% of patients, and the damage is limited to the nail matrix (the tissue under the cuticle where the nail forms). In psoriasis, nail involvement tends to be more extensive and more painful, often including the nail lifting away from the bed and thickening underneath. If you notice pitting alongside skin plaques or patchy hair loss, the nail changes can help confirm what’s driving those symptoms.
Clubbing Points to Heart or Lung Problems
Clubbing is a gradual change in which the fingertips widen and the nails curve downward, wrapping over the tip of the finger like an upside-down spoon. The angle between the nail and the cuticle, normally a slight notch, fills in and becomes flush or bulging.
This happens because low oxygen levels in the blood trigger platelets to cluster in the tiny blood vessels of the fingertips, releasing growth signals that stimulate abnormal tissue and capillary growth. The process reshapes the fingertip over weeks to months.
Clubbing is associated with conditions that reduce blood oxygen levels: chronic lung infections like bronchiectasis and tuberculosis, lung cancer, congenital heart defects, and infective endocarditis (an infection of the heart valves). It also appears in some cases of inflammatory bowel disease and chronic liver disease. Clubbing is rarely subtle once it’s established, and it almost always warrants investigation into what’s driving it.
Dark Streaks and Melanoma Risk
A dark brown or black streak running lengthwise down a nail can be completely benign, especially in people with darker skin tones. But it can also be subungual melanoma, a potentially deadly skin cancer that grows under the nail plate.
Dermatologists use an ABCDEF framework to assess these streaks:
- Age: Most common between ages 50 and 70, and more frequent in people of African, Japanese, Chinese, or Native American heritage
- Band: A brown-black band 3mm or wider with blurred borders
- Change: The band changes in width, color, or shape over time, or doesn’t improve with treatment
- Digit: The thumb, big toe, and index finger are the most commonly affected
- Extension: Pigment spreading into the skin around the nail (called the Hutchinson sign), which suggests aggressive melanoma
- Family history: A personal or family history of melanoma or atypical moles
Any new dark streak under a nail, especially one that’s widening or accompanied by darkening of the surrounding skin, deserves prompt evaluation. Caught early, nail melanoma is treatable. Caught late, outcomes are significantly worse.
Splinter Hemorrhages and Heart Infections
Tiny dark lines that look like splinters trapped under the nail are called splinter hemorrhages. They’re small streaks of blood from broken capillaries in the nail bed. Most of the time, they result from minor trauma, like bumping your hand or working with your fingers.
These lines became famous in the 1920s when they were first described in patients with infective endocarditis, an infection of the heart valves. In reality, they’re a nonspecific finding that shows up in many situations, from everyday injuries to sepsis. Even in confirmed endocarditis cases, hand and foot findings like splinter hemorrhages appear in fewer than 15% of patients. A single splinter hemorrhage on one nail is almost certainly from a bump. Multiple hemorrhages across several nails, especially alongside fever, fatigue, or a new heart murmur, are more concerning.
Thyroid Disease and Brittle Nails
Both overactive and underactive thyroid conditions can cause nails to become brittle, dry, and prone to cracking. In some cases, the nail plate separates from the nail bed, a condition called onycholysis, where the nail lifts up and a white gap appears underneath. Thyroid-related nail changes often accompany other symptoms like unexplained weight changes, fatigue, or sensitivity to temperature. Treating the underlying thyroid imbalance usually allows nails to return to normal as they grow out, though this takes several months given how slowly nails grow.