Understanding Nail Anatomy: The Structure of Fingernails and Toenails
Updated: Oct 28
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Your nails are more than the hard surface you trim and polish. They are part of a "nail unit" with hidden tissues that grow the nail, hold it in place, and seal out germs, and they protect the blood vessels and nerves at the tips of your fingers and toes [1].
Quick Answer: What is nail anatomy?
Nail anatomy is the structure of the nail unit: the visible nail plate plus the tissues around and beneath it, including the matrix that produces the plate, the nail bed, the nail folds and cuticle, and the hyponychium. Nails protect fingertips and toes and aid touch. Unexplained nail changes, especially a dark or red line, should be checked. [1]
What the research says
Most of the tissue under the nail plate is nail bed, not matrix. An anatomy review describes the nail plate as lying on the nail matrix (15-25% of the tissue beneath it) and the nail bed with its onychodermal band (75-85%), with the hyponychium at the free edge (de Berker, Clin Dermatol, 2013 [2]).
Nail problems are common. A 2025 clinical review reports that nail disorders account for 10% of dermatologic disorders, that brittle nails affect up to 20% of the population, and that melanoma typically appears as a longitudinal brown-black nail line but presents as a nail mass in about 30% of cases (Leggit, Am Fam Physician, 2025 [3]).
Dark nail bands in children are rarely cancer. A systematic review and meta-analysis of 24 studies (1,391 children with longitudinal melanonychia) found that nevus was the most common diagnosis (86.3%), only eight cases of subungual melanoma in situ were reported, and no invasive melanomas were identified; this applies to children, and any new or changing dark band in an adult still needs prompt evaluation (Tsai et al., Pediatr Dermatol, 2024 [4]).
What are the parts of the nail unit?
The nail you can see is only one part of the nail unit. The table below lists the main parts, using the terms providers use [1].
Nail part | What it is | Why it matters |
Nail plate | The hard, slightly curved surface of the nail, with subtle top-to-bottom ridges. The free edge is the white tip you trim. | The ridges are unique to you, and even identical twins have different ones. |
Nail matrix | The structure that produces the nail plate, mostly hidden under the skin. | The lunula, the half-moon at the base of the nail, is the only visible part of it. |
Nail bed | The skin under the nail plate. It sticks tightly to the plate and holds it in place. | Small blood vessels here nourish the tips of your fingers and toes. |
Nail folds (paronychium) | The skin that borders each nail: lateral folds at the sides and a proximal fold at the base. | The folds and the plate shield the matrix from ultraviolet (UV) light. |
Hyponychium | The skin and space under the free edge, where the nail bed meets the skin outside. | A strong barrier against germs and irritants, with many immune cells. |
Onychodermal band | A very thin (1 to 1.5 millimeter) band marking the border between the nail bed and hyponychium. | You can see it as a line of color between the pink or darker part of the nail and the white tip. |
Cuticle (eponychium) | A thick layer of skin cells along the proximal nail fold that sticks to the nail plate. | Protects against germs and infection. |
What are fingernails and toenails made of?
Nails are made of specialized skin cells, which is why they are called skin appendages. The nail plate is made mostly of keratin, a protein that keeps nails strong, plus water that keeps them from getting too dry or fragile and fats (lipids) that help water stay in the nail [1].
Nails are not bones. Keratin is the building block of nails, while collagen, a different protein, is the building block of bones [1].
How Fast Do Nails Grow?
Toenails grow more slowly than fingernails, so a damaged toenail takes much longer to grow out than a damaged fingernail.
Nail type | Typical growth | Full regrowth after loss |
Fingernail | About 3 millimeters per month | At least 6 months |
Toenail | About 1.5 millimeters per month | 12 to 18 months |
Toenails grow more slowly than fingernails, so a damaged toenail takes much longer to grow out [1].
What are common nail conditions?
Injuries, infections, skin diseases, and other conditions can change how nails look and feel. Some mainly affect the nails, while others reflect something happening elsewhere in the body [1].
Brittle nails: dry, fragile nails that break easily. Causes include nutritional deficiencies, skin diseases such as eczema or lichen planus, medications, and underlying medical conditions [1].
Ingrown toenails: the nail plate grows into the skin alongside it (or, less often, at its base) [1].
Nail infection (paronychia): bacteria enter broken skin around the nail plate, and frequent dishwashing or nail biting can raise the risk [1].
Toenail fungus (onychomycosis): typically affects the toenails, especially the big toe, and going barefoot around pools and public showers raises the risk [1].
Nail psoriasis: a chronic autoimmune condition that most commonly affects the fingernails [1].
Nail separation (onycholysis): the nail plate separates from the nail bed. Fungal infections, medications, and trauma from repeated manicures and pedicures are common causes [1].
Subungual hematoma: direct trauma, like slamming a finger in a door, makes blood pool beneath the nail plate [1].
Nail cancer (subungual melanoma): a skin cancer of a fingernail or toenail. A brown, black, or red line in the nail is the most obvious symptom, and it needs prompt treatment [1].
What Nail Lines Can Mean
Nail lines are discolored streaks that can run top to bottom or side to side. They can signal a nail disorder or injury, an underlying medical condition, a vitamin or mineral deficiency, or a reaction to a medication [1].
Type of line | Possible causes |
White lines (leukonychia) | Fungal infections, repeated stress on the nails, heart failure, arsenic poisoning, and drug side effects. |
Red lines (longitudinal erythronychia) | On a single nail: noncancerous tumors or cancer. On several nails: conditions such as lichen planus or Darier disease. |
Brown-black lines (longitudinal melanonychia) | Often harmless, and common with age in people with darker skin, but they can also signal an infection, a nail injury, or cancer. |
Beau's lines | Side-to-side grooves, usually a sign that something like stress or illness interrupted nail growth. |
When to See a Provider
Contact a healthcare provider if you notice changes to a nail or the skin around it, such as new color patches, lines or spots, pits or ridges, flaking or peeling, or pain or swelling. Changes in nail color or texture can also be signs of conditions like heart failure, kidney failure, nutritional deficiencies, infection, or heavy metal poisoning, so unexplained changes deserve a check. A dermatologist specializes in skin, nails, and hair, but your primary care provider can also diagnose and treat many nail conditions [1].
How should you care for your nails?
Healthy nail care means leaving cuticles alone, trimming nails straight across, avoiding biting or picking, limiting gel polish, protecting your feet from fungus and moisturizing brittle nails.
Protect the seal: leave your cuticles alone instead of cutting or pushing them back [1].
Trim sensibly: cut nails straight across with just a slight rounding at the tips to lower the risk of an ingrown nail [1].
Be gentle: do not bite or pick at your nails, and wear gloves for dishes and other chores [1].
Give nails a break from polish, and avoid or limit gel polish [1].
Protect your feet: wear comfortable shoes that do not squish your toes, and wear sandals or shoes beside swimming pools and in public showers to help guard against fungus [1].
Moisturize: nail moisturizers with ingredients like petrolatum, lanolin, glycerin, and propylene glycol help hydrate and protect nails, especially brittle ones [1].
Check your nails regularly, and see a provider if you notice anything unusual [1].
What is the bottom line on nail anatomy?
Your nails are a small but hardworking system: the plate you see, the matrix that grows it, the bed that anchors it, and the cuticle, folds, and hyponychium that seal out germs. Treat them gently, leave your cuticles intact, and get unexplained changes checked, especially a new dark line in a single nail [1].
Frequently Asked Questions
What are nails made of?
Nails are made of specialized skin cells. The hard nail plate is mostly keratin, a tough protein, along with water that keeps it from drying out and fats (lipids) that help water stay in the nail.
Are nails bones?
No. Nails are built from keratin, while bones are built from a different protein called collagen.
What is the lunula?
The lunula is the half-moon at the base of the nail, most often seen on the thumbs. It is the only visible part of the nail matrix, the structure that produces the nail plate.
How fast do fingernails grow?
Fingernails typically grow about 3 millimeters per month. If you lose one, full regrowth takes at least six months.
How fast do toenails grow?
Toenails usually grow about 1.5 millimeters per month, roughly half as fast as fingernails. Full regrowth after losing a toenail takes 12 to 18 months.
What does the cuticle do?
The cuticle (eponychium) is a thick layer of skin cells along the proximal nail fold. It sticks to the nail plate and protects against germs and infection.
Is it safe to push back or cut my cuticles?
It is better to leave your cuticles alone. Pushing back or removing them during manicures and pedicures can harm your nail health.
What is paronychia?
Paronychia is a nail infection that happens when bacteria enter broken skin around the nail plate. Frequent dishwashing and nail biting can raise the risk because they dry or break the skin.
What do lines in my nails mean?
Nail lines have many causes, from minor injuries that heal on their own to medical conditions that need treatment. The color and direction of the line help a provider narrow down the cause, so see one if a line has no known cause.
Which nail changes need prompt attention?
A brown, black, or red line in a nail on a single finger or toe can be a sign of nail cancer (subungual melanoma), which needs prompt diagnosis and treatment. Pain or swelling around the nail, new pits or ridges, and flaking or peeling also deserve a visit to a provider.
Related Resources
Related reading on Rinnit:
External resources for deeper reading:
References
Cleveland Clinic. Nails (Fingernails, Toenails). Cleveland Clinic. Last updated September 17, 2025. https://my.clevelandclinic.org/health/body/nail-anatomy
de Berker D. Nail anatomy. Clin Dermatol. 2013;31(5):509-515. PMID 24079579. https://doi.org/10.1016/j.clindermatol.2013.06.006
Leggit JC. Nail abnormalities. Am Fam Physician. 2025;112(4):401-409. PMID 41118185. https://pubmed.ncbi.nlm.nih.gov/41118185/
Tsai SY, Hamilton CE, Mologousis MA, et al. Melanoma-like features in pediatric longitudinal melanonychia: a systematic review and meta-analysis. Pediatr Dermatol. 2024;41(4):613-620. PMID 38500311. https://doi.org/10.1111/pde.15597
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last updated in September 2025.
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