Human nails are made mostly of a tough protein called keratin. Keratin is the same material that forms hair and the outer layer of skin. Nails are made of several layers of dead, flattened cells packed with keratin. These cells are produced by the nail matrix at the base of the nail and are pushed forward as new cells form.
What Are Human Nails Made Of? Simplified
Nails are built from a protein called keratin. Keratin is a fibrous structural protein that gives nails strength and flexibility. The nail plate — the hard part you see — consists of about 15 to 20 layers of dead, keratinized cells. These cells are tightly compressed and linked by disulfide bonds, which make nails hard but slightly flexible.
Keratin in nails is different from keratin in hair or skin. Nail keratin has a higher sulfur content from the amino acid cysteine. More cysteine means more disulfide bonds, which makes nails tougher than hair. This is why you can bend a strand of hair without breaking it but a nail will snap under enough pressure.
What Are the Main Parts of a Nail?
Understanding the parts helps explain how nails are made. The nail matrix sits under the skin at the base of the nail, just behind the cuticle. This is where new nail cells are made. The matrix produces keratinocytes — cells that fill with keratin and then die and flatten.
The nail plate is the visible hard surface. It rests on the nail bed, which is living skin with blood vessels and nerves. The nail bed supplies nutrients to the growing nail. The lunula is the pale half-moon shape at the base of the nail plate. It is the visible part of the matrix. The cuticle seals the space between the nail plate and the skin, protecting the matrix from infection. The hyponychium is the seal under the free edge of the nail.
How Do Nails Grow?
Growth happens in the matrix. Cells divide, push older cells forward, and those older cells fill with keratin, die, and harden. Fingernails grow about 3 millimeters per month on average. Toenails grow much slower — roughly 1 millimeter per month. Growth is faster in younger people, in summer, and on the dominant hand. Injury to the matrix can slow growth temporarily or cause permanent ridges.
It takes about 6 months for a fingernail to fully replace itself from base to tip. Toenails take 12 to 18 months. Because the nail plate is made of dead cells, once it leaves the matrix it cannot repair itself. Damage to the visible nail plate stays until the nail grows out.
What Gives Nails Their Strength and Flexibility?
Two factors: keratin structure and water content. The disulfide bonds in keratin provide hardness. The natural moisture in nails — about 10 to 15 percent water — gives them flexibility. If nails lose too much water, they become brittle and crack. If they absorb too much water, they become soft and weak. This is why frequent hand wetting and drying cycles can damage nails.
Nails also contain small amounts of lipids and calcium. Calcium is not what makes nails hard. That is a common myth. The hardness comes from keratin. Nails do contain calcium, but only trace amounts — about 0.1 percent by weight. Adding more calcium to your diet will not make nails harder.
Can Diet Affect Nail Strength?
Yes, but the evidence is limited for most supplements. Protein intake matters because nails are made of protein. A diet deficient in protein can lead to slower growth and weaker nails. Iron deficiency can cause spoon-shaped nails. Zinc deficiency can cause white spots and poor growth.
Some research suggests biotin — a B vitamin — may improve nail thickness in people with brittle nails. Most studies are small and not conclusive. No large clinical trial has confirmed that biotin supplements help healthy nails. The same caution applies to collagen, silica, and other marketed nail supplements. While the biology is plausible, the evidence for benefit in people without a deficiency is not strong.
What Causes Nails to Change Color or Texture?
Changes in nail color or texture can come from injury, infection, or underlying illness. White spots are usually from minor trauma to the matrix — not a calcium deficiency. Yellow nails can result from fungal infection, smoking, or certain medications. Dark streaks under the nail should be checked by a doctor, as they can sometimes signal melanoma.
Ridges running from cuticle to tip are a normal part of aging. Horizontal grooves, called Beau’s lines, appear after a serious illness or injury that temporarily stops nail growth. Pitted nails — small dents — are common in psoriasis. Nail changes alone rarely diagnose a disease, but they can prompt a doctor to look further.
Frequently Asked Questions
Are fingernails and toenails made of the same thing?
Yes. Both are made of keratin with the same basic structure. Toenails have a slightly different keratin composition that makes them denser and stronger.
Is the white part of the nail different from the rest?
No. The white free edge at the tip is the same keratin as the rest of the nail plate. It appears white because it has detached from the nail bed beneath it, so you see air instead of pink tissue.
Do nails need to breathe?
No. Nails are dead cells and do not need oxygen. The living nail bed below gets oxygen from blood, not from air. Covering nails with polish or artificial nails does not suffocate them.
What causes brittle nails?
Brittle nails are usually from repeated wetting and drying, harsh chemicals, or low humidity. Less often, they can be a sign of thyroid disease or a nutritional deficiency. Brittle nails alone are rarely a sign of serious illness.
