What your nails say about your health and how to fix them

Nails are far more than an aesthetic detail. Their color, texture, and shape can reveal everything from nutritional deficiencies to organ disease that might otherwise go unnoticed. This guide from a clinical dermatology perspective covers nail anatomy, how to read the signals your nails send, and the daily habits that actually make a difference.

Nail anatomy

Nails are a five-part system: the nail plate (the hard, visible surface), the nail bed (the pink tissue underneath), the matrix (the "factory" that generates every nail cell), the cuticle (the seal between the plate and the matrix), and the nail folds, including the hyponychium at the distal tip.

The nail plate is roughly half a millimeter thick and made of layers of keratin, the same protein found in hair. Fingernails grow approximately 3 mm per month, so a full nail takes three to five months to grow out entirely.

What color and texture reveal

Ridges and lines

Vertical ridges (onychorrhexis) become more common with age and are usually benign, though a sudden worsening may point to thyroid dysfunction or iron-deficiency anemia. Horizontal lines, known as Beau's lines, indicate that the matrix briefly paused its activity in response to a severe physical stressor: high fever, surgery, trauma, or serious illness. Because nails grow at roughly 3 mm per month, the distance of the line from the base gives a timeline of when the event occurred.

White spots and the calcium myth

Scattered white spots (leukonychia punctata) do not mean calcium deficiency. They are almost always the result of minor trauma that briefly disrupted even keratin production in the matrix and typically grow out on their own. True leukonychia, where the entire nail turns white, can be associated with low albumin. Terry's nails, where the proximal two-thirds are white with a pink distal band, can signal liver disease, heart failure, or diabetes.

Yellow nails

The most common cause is onychomycosis, a fungal infection that also makes nails crumbly. If the skin and whites of the eyes are also yellowing, liver disease must be ruled out. Yellow nail syndrome, a rare triad of yellow nails, leg swelling, and pulmonary involvement, is caused by reduced lymphatic drainage and impaired oxygenation.

Why nails break and peel

There are three types of brittleness:

• Dry brittleness: excessive handwashing, alcohol sanitizers, and dry environments strip moisture, making the plate rigid and prone to snapping.
• Soft brittleness: repeated wet-dry cycles break down the lipid cement between keratin layers, causing the nail to flex and bend until it tears.
• Chemical brittleness: prolonged use of formaldehyde-based nail hardeners or frequent acetone exposure damages the keratin structure over time.

Systemically, hypothyroidism slows keratin production and iron-deficiency anemia is the most underdiagnosed deficiency affecting nails, especially in women. Severe deficiency can cause koilonychia, where the nail curves upward like a spoon. Nail peeling (lamellar onychoschizia) is usually the result of repeated wet-dry exposure and, less commonly, iron or vitamin B12 deficiency.

The biotin myth

Biotin is the automatic answer to nearly every nail complaint, but true biotin deficiency is extremely rare. Worse, excess biotin supplementation can interfere with thyroid lab values, masking abnormal results. The deficiency with real clinical impact is iron: check ferritin, serum iron, and a complete blood count before taking any supplement.

Daily nail care habits

Cutting and filing

Use sharp scissors or quality nail clippers. Dull tools crush the plate and cause micro-splits before the cut is even made. Cut straight across and gently round the corners. File in one direction only. The back-and-forth motion separates the nail plate layers and causes peeling.

Hydration

Urea at 10-20% is the most effective ingredient for penetrating the nail plate and maintaining flexibility. Petroleum jelly or lip balm applied after handwashing seals residual moisture. Cuticle oil works mainly as a barrier for the nail fold, not as a deep moisturizer for the nail plate itself.

Protection and cuticles

Wear gloves for dishwashing, cleaning, and chemical exposure. Reduce acetone use and minimize the activities that alternate the nail between wet and dry states.

The cuticle is the only barrier protecting the matrix from bacteria and fungi. Cutting it removes that protection entirely. Safer alternatives include soaking fingers first to soften the cuticle and gently pushing it back with a wooden stick, or applying a KOH-based cuticle remover that dissolves only dead tissue without breaking the living seal.

Final thoughts

Nail health reflects what is happening inside the body. Before reaching for supplements, observe the pattern of change, assess context such as thyroid function, iron levels, and protein intake, and build the daily mechanical habits described here. Retention, not growth speed, is the key to long, strong nails.