Nails are hard, protective plates made of keratin, the same tough protein found in hair. They grow from a hidden structure called the matrix, tucked under the skin at the base of each finger and toe, and serve as natural armor for the sensitive nerve endings and tiny bones at your fingertips and toes. Though they seem simple, nails are surprisingly complex structures that reveal a lot about your overall health.
What Nails Are Made Of
Every nail has three main parts that work together. The nail plate is the hard, slightly curved surface you can see. It’s mostly smooth but has subtle ridges running from base to tip. The white tip you trim is called the free edge.
Beneath the plate sits the nail bed, a layer of skin packed with small blood vessels that nourish your fingertips and toes. The bed has tiny ridges that interlock with matching ridges on the underside of the nail plate, creating a strong bond that keeps the nail firmly attached.
The nail matrix is the factory. Mostly hidden under your skin, it produces specialized cells that harden into the nail plate as they’re pushed forward. The only visible part of the matrix is the lunula, that pale half-moon shape at the base of your thumbnail (and sometimes your other nails). The basic anatomy is the same for both fingernails and toenails.
Why Humans Have Nails
Our nails evolved from the sharp claws of tree-dwelling ancestors. Living high in forest canopies meant gripping branches without slipping, and needle-like talons weren’t suited for that job. Over millions of years, those pointed claws flattened and widened into the broad nails we have today, giving early primates a better grip on limbs and safer movement through the trees.
In modern humans, nails still serve real purposes. They protect vulnerable nerve endings, blood vessels, and the small bones at the tips of your fingers and toes from cuts, crushing injuries, and infection. Toenails in particular help with balance and stability when walking. Fingernails also provide counter-pressure when you touch or grip objects, which is why picking up a coin or peeling a sticker feels nearly impossible when a nail is missing.
How Fast Nails Grow
Fingernails grow roughly 3.47 mm per month, while toenails lag behind at about 1.62 mm per month. That means a fingernail takes three to five months to grow from the matrix to the free edge, while a big toenail can take over a year to fully replace itself. A study in the Journal of the European Academy of Dermatology and Venereology found that nail growth rates have actually increased compared with estimates from decades ago, possibly due to improved nutrition.
Several factors speed up or slow down growth. Nails grow faster in younger people and tend to slow with age. Pregnancy increases growth speed and produces thicker nail plates, likely driven by hormonal shifts and increased blood circulation. The middle finger typically grows the fastest nail, while the pinky is the slowest. Nails also grow faster in summer than in winter.
What Your Nails Can Tell You About Health
Changes in nail shape, color, or texture sometimes signal problems elsewhere in the body. One of the most well-known examples is nail clubbing, where the fingertips swell and the nails curve downward around them. Clubbing is strongly associated with lung diseases, particularly lung cancer and bronchiectasis (chronic airway damage). It can also appear with cyanotic heart disease, inflammatory bowel disease, celiac disease, and liver cirrhosis. In over 90% of cases linked to a condition called hypertrophic osteoarthropathy, the underlying cause is a lung malignancy or chronic lung infection. Clubbing can even appear before a lung disease is formally diagnosed.
Spoon-shaped nails, where the nail dips inward like a small scoop, are called koilonychia. This is most often a sign of iron deficiency anemia. People with vitamin B deficiencies may also develop them. If your nails have taken on a concave shape, checking your iron levels is a reasonable next step.
Fungal Infections
Nail fungus is one of the most common nail disorders. At least half of abnormal-looking toenails turn out to be fungal infections, with overall prevalence estimated between 1% and 8% of the population. Toenails are hit far harder than fingernails because fungi thrive in the warm, moist environment inside shoes.
The most common form starts at the tip or side of the nail and works its way back, causing the nail to lift from the bed, thicken, and crumble. A less common type appears as white, chalky patches on the nail surface. The rarest form begins near the base of the nail, closest to the cuticle. Left untreated, any of these can progress to total nail destruction.
Chemicals in Nail Products
Nail polish has historically contained three problematic ingredients, sometimes called the “toxic trio.” The first is a resin that can release residual formaldehyde, classified as a carcinogen. Even trace amounts as low as 0.006% can trigger allergic skin reactions in sensitive individuals. The second is a plasticizer called DBP, which animal studies linked to reproductive and developmental toxicity. The European Union banned it in 2004, and some U.S. states followed. The third is toluene, a solvent that can affect the nervous system, cardiovascular system, and reproductive health.
Since the 1990s, regulations have pushed these chemicals out of most major nail polish brands. Many products now advertise themselves as “3-free,” “5-free,” or higher, meaning they’ve removed these and additional chemicals. If you use nail products frequently, especially in a professional salon setting with limited ventilation, choosing formulas that exclude these ingredients reduces your exposure.
How to Trim Nails Properly
The American Academy of Dermatology recommends trimming nails right after a bath or shower, when they’re soft and less likely to crack or split. If that’s not convenient, soaking them in lukewarm water for a few minutes works too. Use a standard nail clipper for fingernails and a larger toenail clipper for toenails.
For fingernails, cut almost straight across, then use a file or emery board to gently round the corners. This keeps them strong and prevents snagging on fabric. For toenails, cut straight across without rounding the corners, which is the single most effective way to prevent ingrown toenails. When filing, always move in one direction rather than sawing back and forth, since the friction of back-and-forth filing weakens the nail.
One common mistake is trimming or pushing back the cuticles. Cuticles seal the gap between your skin and the nail plate, blocking bacteria and other germs from reaching the nail root. Cutting them opens a pathway for infection.