What makes your fingernails and hair keep growing?

Introduction

Fingernails and hair are parts of our bodies that keep growing throughout much of life. At first glance this seems simple: cut your nails or get a haircut and they grow back. But the reason they grow involves specialised cells, repeating cycles, hormones, nutrition, and genetics. This article explains how and why nails and hair continue to grow, what controls their speed, and common factors that change growth.

Quick answer: why nails and hair keep growing

Both fingernails and hair are made primarily of a tough protein called keratin produced by living cells in specialised structures (nail matrix and hair follicles). Cells in these structures divide and push older cells outward; those older cells harden into the visible nail plate or hair shaft and are effectively “dead” tissue. Continuous production by the underlying living tissue causes apparent ongoing growth until a growth cycle pauses or the structure is removed.

Anatomy and basic biology: where growth starts

Hair: follicles and the hair bulb

Every hair grows from a hair follicle, a tiny pocket in the skin. At the base of the follicle is the hair bulb, where actively dividing cells (matrix keratinocytes) create the hair shaft. As new cells form, older cells are pushed up and away, keratinise (fill with keratin protein), lose their nuclei and become the non-living hair shaft that protrudes from the skin.

The hair follicle also contains pigment-producing cells (melanocytes) that give hair its color and a surrounding supply of blood vessels that provide nutrients and hormones needed for cell division.

Nails: the nail matrix and nail plate

Fingernails and toenails grow from the nail matrix, a layer of cells located under the cuticle and behind the visible lunula (the crescent-shaped pale area). Cells in the matrix divide continuously and new cells are pushed forward, flattening and hardening into the nail plate. The nail bed beneath the plate supports it as it grows out over the fingertip.

Unlike skin, the visible nail and hair are composed of dead, densely packed keratin cells. What keeps growth going is the living tissue underneath that keeps making new cells.

The role of the growth cycle

Hair growth phases

Hair growth is cyclical and consists of three main phases: anagen (growth), catagen (transition), and telogen (resting). During anagen, follicles actively divide and hair lengthens; this phase can last years on the scalp but is shorter on arms or legs. Catagen is a brief shrinking phase during which growth slows and the follicle separates from its blood supply. Telogen is a resting phase when the hair is eventually shed and a new anagen phase begins.

Because different follicles are in different phases at any time, overall hair cover remains steady even though individual hairs are shed and replaced.

Nail growth pattern

Nails do not follow the same clear-cut cyclical phases as hair. The nail matrix continuously produces cells, so nails grow steadily until an interruption—such as injury, illness, or nutritional deficiency—reduces production. Growth rates can slow with age or change because of health, but there isn’t a synchronized shedding cycle like hair.

What determines growth speed?

Genetics and individual variation

Inherited traits strongly influence how fast your hair and nails grow. Genetics determine the typical anagen phase length for scalp hair, average hair thickness, nail shape, and baseline growth rate. Some people naturally have faster-growing nails or hair due to inherited differences in cell activity and follicle behaviour.

Age

Growth rates change with age. Children’s nails and hair often grow faster than older adults’. Hair anagen phases tend to shorten with age, producing thinner, slower-growing hair. Nail growth also slows after middle age, and nails may become more brittle.

Hormones

Hormones are powerful modulators. Androgens (male sex hormones) influence hair growth patterns—stimulating facial and body hair in some areas while contributing to scalp hair thinning in genetically susceptible people. Thyroid hormones affect overall metabolic rate and cell turnover: both hyperthyroidism and hypothyroidism can change hair and nail growth and quality. Pregnancy often alters hair and nail growth because of shifts in hormone levels, sometimes causing faster nail growth and thicker hair.

Nutrition and overall health

Proper nutrition supplies the raw materials for cell division and keratin production. Protein, iron, zinc, certain B vitamins (including biotin), and other micronutrients are important for healthy hair and nails. Severe or prolonged nutritional deficiencies can slow growth, cause brittle nails, or make hair thin and more easily shed. However, normal variations in diet cause modest effects; only significant deficiencies create major changes.

Blood flow and circulation

Active blood supply to follicles and nail matrices delivers oxygen, nutrients, and hormones. Conditions that reduce circulation—such as peripheral vascular disease or cold exposure—can slow growth. Conversely, good circulation supports cell division and healthy growth.

Common factors that change growth or appearance

Illness, stress, and medication

Severe illness, major surgery, or high stress can push hair follicles into the telogen (resting) phase, producing increased hair shedding a few months later — a condition called telogen effluvium. Nails may show transverse ridges (Beau’s lines) after serious systemic stress because the matrix temporarily pauses cell production. Certain medications, including chemotherapy drugs, can halt cell division in hair and nails, causing hair loss or nail changes.

Local damage and injury

Trauma to a nail matrix can permanently or temporarily change nail growth—causing deformities, slow growth, or ridging. Repeated friction or damage to hair (tight hairstyles, chemical treatments, heat) can break hair shafts and give the impression of slow growth even when follicles remain active.

Seasonal and lifestyle effects

Many people notice hair and nails grow a bit faster in summer. This may result from increased circulation, warmer temperatures, and more sunlight (which affects hormones and vitamin D). Smoking and poor sleep are associated with poorer nail and hair health; quitting smoking and improving sleep and diet generally helps, though results vary.

Differences between fingernail and hair growth

While nails and hair are both made of keratin, they differ in structure, growth rates, and cycles. Fingernails grow continuously (averaging about 2–4 mm per month for fingernails, slower for toenails), whereas hair growth is cyclical with distinct growth and rest phases. Hair is anchored in follicles deep in the skin, while nails are flat plates produced by a specialized matrix. These differences explain why nails don’t shed regularly like hair and why scalp hair can reach much greater lengths than body hair.

Measuring and observing growth

You can roughly track nail growth by marking the nail near the cuticle and checking how far the mark moves over a month. For hair, measuring length over time or photographing the same angle under similar conditions gives a sense of rate. Remember that growth is variable—affected by seasons, health, and age—so short-term measurements may not reflect long-term trends.

When to see a healthcare professional

If you notice sudden, severe changes—rapid hair loss, pronounced thinning, marked slowing of nail growth, new ridges or splitting, discoloration, or deformity—it’s reasonable to consult a healthcare provider. Such signs can sometimes indicate nutritional deficiencies, thyroid disease, autoimmune conditions, fungal infections, or other treatable medical problems that affect the follicles or nail matrix.

Doctors usually assess medical history, diet, medications, and do a physical exam; in some cases they may order blood tests (for iron, thyroid function, vitamin levels) or refer to a dermatologist.

Practical lifestyle steps that support healthy growth

While genetics set a baseline, some straightforward habits support optimal hair and nail growth and reduce damage:

Maintain a balanced diet with adequate protein, iron, zinc, and B vitamins. If you suspect a deficiency, consult a health professional before taking supplements.

Avoid repeated mechanical damage: use gentle nail trimming, avoid aggressive manicures, and limit tight hairstyles or harsh chemical treatments that break hair.

Protect nails and hands from prolonged wet exposure and harsh detergents—wear gloves for cleaning tasks to prevent brittleness.

Manage chronic conditions and medications with your doctor’s guidance—treating underlying thyroid disease or improving circulation can help restore normal growth.

Allow time: hair and nails grow slowly in human terms. Expect gradual improvements rather than quick fixes.

Common misconceptions

Cutting hair or nails does not make them grow faster. Trimming reduces split ends and breaks that give the appearance of slower growth, but it does not change the rate at which the follicle or matrix produces new cells.

There is no widely proven “miracle” supplement that reliably speeds up hair or nail growth in healthy people. Some nutrients help if there is a deficiency; otherwise effects are limited.

Relevant examples

Example 1: Pregnancy often prolongs the anagen phase for scalp hair, so many pregnant people notice thicker hair and less shedding. After childbirth, hair often enters telogen and temporary increased shedding can occur.

Example 2: A person recovering from a severe illness may develop Beau’s lines—horizontal grooves across nails—because the nail matrix paused production during the health crisis. Over months the nail grows out and the line moves toward the tip.

How this knowledge is used

Understanding growth mechanisms helps dermatologists diagnose causes of hair loss or nail changes, and guides recommendations: dietary adjustments for deficiencies, topical or systemic treatments for certain conditions, and behaviour changes to prevent mechanical damage. It also informs cosmetic choices like timing trims or treatments based on natural cycles.

Conclusion

Fingernails and hair keep growing because living cells in the nail matrix and hair follicles continuously divide and produce keratinised cells that are pushed outward and hardened. Growth speed is controlled by genetics, hormones, nutrition, blood supply, age, and external factors such as injury or stress. While you cannot fundamentally override your genetic baseline, good nutrition, gentle care, and managing health conditions can support healthier, stronger growth over time.