Fingernails are made primarily of keratin, a tough structural protein that also forms hair and the outer layer of skin. But the nail plate isn’t just one type of keratin. It contains a unique blend of two different keratin types, along with water, a small amount of fat, and trace minerals that together create the hard, flexible shield at your fingertips.
The Two Types of Keratin in Your Nails
Your nails contain both skin-type keratins and hair-type keratins, which makes them structurally distinct from either skin or hair alone. The skin-type keratins are softer and easier to extract from nail tissue in laboratory settings, while the hair-type keratins are more tightly bonded and resistant to breakdown. This combination is what gives nails their particular balance of hardness and slight flexibility. If nails were made only of the harder hair-type keratin, they’d be more brittle. If they contained only the softer skin-type, they wouldn’t hold up to daily use.
These two keratin types aren’t evenly distributed. In the deeper layers of the nail matrix (where nails are produced), skin-type and hair-type keratins occupy separate zones. Near the surface, both types are co-expressed in the same cells. This layered architecture helps explain why a nail can bend slightly under pressure without snapping, yet still resist scratching and abrasion.
Beyond Protein: Water, Lipids, and Minerals
Keratin dominates the nail plate, but it’s not the whole story. Healthy nails contain roughly 7 to 18 percent water by weight, with an average around 12 percent. That water content matters more than you might expect. When nails lose too much moisture, they become rigid and prone to cracking. When they absorb too much (from prolonged soaking, for instance), they soften and peel.
Lipids, or fats, make up less than 5 percent of the nail plate. These fats are organized in a layered structure running parallel to the nail surface, which helps control how water moves in and out of the nail. Think of them as a moisture barrier built into the nail itself.
Trace minerals round out the composition. The nail plate contains magnesium, calcium, iron, zinc, sodium, and copper. One common misconception is that calcium makes nails hard. It doesn’t. Calcium accounts for only about 0.2 percent of the nail plate by weight. The hardness comes from the keratin structure and the sulfur-based bonds holding it together. Magnesium, on the other hand, plays a more noticeable role in nail quality: people with low magnesium levels tend to develop soft, flaky nails that split or break easily.
How Your Nails Are Built
Every nail starts in the nail matrix, a crescent of tissue tucked under the skin just behind the cuticle. The matrix is the factory. Specialized cells there divide, fill with keratin, then flatten and lose their nuclei as they’re pushed forward. By the time these cells reach the visible nail plate, they’re dead, compacted, and fused into the hard surface you can see. About 90 percent of nail growth comes from the germinal matrix, the back portion of this factory. The remaining 10 percent comes from the sterile matrix, which sits closer to the nail bed and plays a bigger role in keeping the nail attached to the skin underneath.
The nail bed, the pink skin visible through your nail, doesn’t produce the nail plate itself. Instead, it provides a surface for the nail to glide along as it grows. The pink color you see is actually blood flowing through the capillaries in the nail bed, visible through the translucent nail plate above.
How Fast Nails Grow
Fingernails grow at an average rate of 3.47 millimeters per month, which is more than twice the speed of toenails (1.62 millimeters per month). At that pace, a fingernail takes roughly four to six months to grow from the matrix to the free edge.
Growth rate varies by finger. Your middle finger typically grows the fastest nail, while your thumbnail and pinky grow the slowest. Age is the most reliable factor: nail growth tends to slow as you get older. The effect of climate is debatable. A famous self-study by American doctor William Bennett Bean, who tracked his own fingernail growth for 35 years starting in 1941, concluded that season and location had no effect. Other research has found a slight increase during summer months, possibly because warmer temperatures increase blood flow to the fingertips.
What Your Nails Reveal About Your Health
Because nails are built slowly over months, they can record disruptions to your health like a timeline. Horizontal dents running across the nail, called Beau’s lines, form when the matrix temporarily slows its cell production. This can happen after a severe illness, a high fever, or certain medications. The dent grows out with the nail, so its position tells roughly when the disruption occurred.
Iron deficiency can thin the nail plate and, in more advanced cases, cause nails to curve upward into a spoon shape. This happens because the nail structure doesn’t have enough support to maintain its normal gentle arc. Nails that turn entirely white except for a narrow pink band at the tip can signal liver or kidney problems. Half-and-half nails, where the bottom half is white and the top half is pink or brown, are associated with kidney disease.
Clubbing, where the fingertips swell and the nail curves downward over them, develops when fibrous tissue builds up beneath the nail. The angle where the nail meets the cuticle increases beyond its normal range. Clubbing is linked to heart and lung conditions that reduce oxygen levels in the blood, though it can also occur without any underlying disease.
These visible changes happen because the nail plate is a direct product of your body’s metabolic state. Any condition that affects protein production, mineral balance, or blood flow to the fingers can leave its mark on the keratin structure being laid down in the matrix.