Healthy nails are smooth, consistent in color, and free of dents or discoloration. They grow at a steady rate of about 3.5 millimeters per month for fingernails and 1.6 millimeters per month for toenails. If your nails look different from what you’re used to, or you’ve noticed changes you can’t explain, a closer look can tell you a lot about what’s going on in your body.
What a Healthy Nail Looks Like
A healthy fingernail has a pinkish tone across the nail bed, which comes from the blood vessels underneath. The surface is smooth with no obvious bumps, pits, or grooves. The nail itself feels firm but slightly flexible, not brittle or paper-thin. At the base, you may see a pale, whitish half-moon shape called the lunula. It’s usually most visible on your thumbs and may be barely noticeable on your other fingers.
Not seeing a lunula isn’t automatically a problem. It tends to be more prominent when you’re young and often shrinks or hides beneath the cuticle with age. If your lunulae have always been subtle or invisible, that’s typical. A sudden change in their appearance, though, is worth paying attention to.
The skin around your nails matters too. Healthy cuticles seal the gap between your nail and your skin, keeping bacteria and fungi out. They should look smooth and moisturized, not cracked, red, or swollen.
A Quick Test for Circulation
You can check blood flow to your nails with a simple test. Press down firmly on the tip of a fingernail for a few seconds until the nail bed turns white, then release. The pink color should return in less than two seconds. A slower return can suggest poor circulation or dehydration.
Another self-check is the Schamroth window test, which screens for nail clubbing (a condition where the fingertips swell and the nails curve downward). Place two matching fingernails from opposite hands back to back. You should see a small diamond-shaped gap between the nail beds. If that window is missing and the nails press flush against each other, clubbing may be present. Clubbing is sometimes linked to heart or lung conditions.
What Nail Color Can Tell You
Small white spots are one of the most common nail changes, and they’re usually harmless. The most frequent cause is minor trauma: bumping your nail against something, wearing tight shoes, or even biting your nails. An allergic reaction to nail polish, hardener, or polish remover can also trigger them. These spots grow out on their own as the nail grows.
Less commonly, white spots appear as a side effect of certain medications or as a rare symptom of systemic conditions like diabetes, liver disease, or psoriasis. If white spots show up repeatedly without an obvious injury, it could point to a zinc deficiency, which contributes to degeneration of the nail plate.
Yellow or greenish nails often signal a fungal infection. Infected nails typically look thickened, crumbly, or slightly lifted from the nail bed. A vitamin B12 deficiency can cause bluish discoloration or dark streaks running lengthwise across the nail. Brownish pigmentation is another possible sign of B12 deficiency. Any new dark streak under a nail that appears without trauma, especially a single streak on one nail, should be evaluated by a dermatologist.
Ridges, Pits, and Grooves
Vertical ridges running from the base of the nail to the tip are extremely common and usually a normal part of aging. They can also appear with iron or magnesium deficiency. On their own, they rarely indicate anything serious.
Horizontal lines or grooves are a different story. Deep horizontal dents, called Beau’s lines, form when nail growth is temporarily interrupted. This can happen after a severe illness, major surgery, or a period of significant physical stress. The groove grows out slowly as the nail moves forward, and once it’s gone, the nail looks normal again. Horizontal ridges can also result from exposure to toxic heavy metals like arsenic.
Small dents or pits scattered across the nail surface are associated with psoriasis and alopecia areata (an autoimmune condition that causes hair loss). Pitting makes the nail look like it’s been poked with a pin. If you notice pitting along with skin changes or hair loss, those conditions may be worth investigating.
Changes in Nail Shape
Nails that gradually flatten and then develop a scooped-out, concave shape are called spoon nails. The indentation can become deep enough to hold a drop of water. This is most often a sign of iron deficiency anemia. It tends to develop slowly: the nail flattens first, and the spoon shape follows over weeks or months.
Spoon nails have also been linked to diabetes, thyroid disorders, lupus, and Raynaud’s phenomenon. Occasionally, a fungal infection can cause the same shape change. If your nails are curving inward, checking your iron levels is a reasonable first step.
Brittle, Peeling, or Splitting Nails
Nails that crack, peel at the edges, or split lengthwise are dealing with what dermatologists broadly call brittle nail syndrome. The two main patterns are longitudinal ridging and splitting (where the nail cracks along its length) and lamellar splitting (where thin layers peel off at the free edge of the nail, like pages of a book).
Environmental causes are the most common culprit. Repeated cycles of wetting and drying your hands weaken the bonds between nail cells. Frequent use of nail polish remover, cuticle removers, and other dehydrating chemicals does the same thing. People who wash their hands frequently for work, get regular manicures, or smoke are at higher risk. Long-lasting gel polishes cured under UV lamps have been reported to thin the nail bed over time.
Nutritional deficiencies also play a role. Brittle nails have been associated with low levels of iron, biotin, vitamin C, folate, and zinc. Biotin supplementation has the most evidence behind it for improving nail strength specifically. A diet low in protein can weaken nails as well, since the nail plate is built primarily from a protein called keratin.
When brittleness appears alongside other symptoms, it can occasionally point to underlying conditions like thyroid disease, anemia, psoriasis, or circulatory problems. But for most people, the fix is more mundane: reduce chemical exposure, keep nails moisturized, and address any gaps in nutrition.
Signs of Infection Around the Nail
An infection of the skin surrounding the nail, called paronychia, shows up as redness, swelling, and tenderness along the nail fold. The area feels warm to the touch, and a pocket of white or yellowish pus may form. Left untreated, the nail itself can start growing abnormally, developing ridges or a wavy surface. In severe cases the nail turns yellow or green, becomes dry and brittle, and can eventually detach from the nail bed.
Paronychia often starts with a small break in the skin, like a hangnail or a cut from aggressive cuticle trimming. Keeping your cuticles moisturized reduces the risk. If your cuticle area is cracked and dry, applying lotion to the nail fold regularly helps maintain that protective seal.
Nutrients That Support Nail Health
Several specific deficiencies leave visible traces on your nails. Iron deficiency can cause vertical ridges or spoon-shaped nails. Zinc deficiency shows up as white spots and overall nail plate deterioration. Low folate makes nails rigid and brittle. Vitamin C deficiency slows nail growth and increases brittleness. And vitamin B12 deficiency can change nail color entirely, producing blue tones or dark streaks.
Biotin, a B vitamin found in eggs, nuts, and whole grains, has the strongest track record for improving brittle nails. Iron-rich foods like red meat, lentils, and spinach support normal nail shape and growth. Zinc from shellfish, seeds, and legumes helps maintain the integrity of the nail plate. Protein from any source provides the raw building blocks for nail growth. If your nails have changed and your diet has been limited, nutritional gaps are one of the most fixable explanations.