Fingernails and toenails are more than just decoration or protection – they can be a window into your health. Brittle, discolored, or deformed nails are often not just a cosmetic problem, but can indicate nutritional deficiencies, illnesses, or lifestyle factors.

Nails consist mainly of keratin, a protein that also forms hair and the outer layer of skin. They grow from the nail matrix beneath the cuticle and reflect the health and nutrient supply at the time of their formation. Since fingernails grow approximately three to six millimeters per month, the nail essentially provides a record of the past few months.

Healthy nails are smooth, uniformly pink with a whitish half-moon at the base, firm yet flexible, and grow evenly. Deviations from this can provide clues – sometimes harmless, sometimes indicating treatable problems.

This guide explains which nutrients are important for healthy nails, what nail changes can indicate, and what you can practically do to strengthen your nails. It's important to remember: not every nail change is cause for panic, but persistent or significant changes should be checked by a doctor.

Nail health is closely linked to overall health. What's good for the body – a balanced diet, sufficient sleep, stress management – ​​is also reflected in the nails. Conversely, weak nails can be an early warning sign that warrants closer attention.

To understand and address nail problems effectively, a basic understanding of the nail's structure is helpful.

The nail matrix lies beneath the cuticle and is the nail's 'production center'. Here, the keratin cells that form the nail are created. The health of the matrix determines the quality of the nail. Damage to the matrix (due to injury, illness, or malnutrition) can lead to permanent nail changes.

The nail plate is the visible part of the nail – what we call the 'nail'. It consists of keratinized, dead cells and is normally about 0.5 mm thick. The nail plate itself is not living and cannot absorb nutrients – which explains why topical 'nail-strengthening' products have limited effectiveness.

The nail bed lies beneath the nail plate and supplies it with nutrients and moisture. The pink color of healthy nails comes from the blood vessels in the nail bed, which are visible through the transparent nail plate.

The lunula is the white crescent at the base of the nail – the visible part of the nail matrix. The lunula is not visible in everyone; this is usually harmless.

The cuticle protects the delicate matrix from bacteria and fungi. Removing or damaging it can promote infections.

Fingernails grow about three to four millimeters per month, toenails more slowly (about one millimeter). Growth slows with age, poor circulation, and malnutrition. A fingernail takes about six months to completely regenerate.

Nails need specific nutrients to grow strong and healthy. A deficiency can manifest as brittle, splitting, or slow-growing nails.

Biotin (vitamin B7) is the star among nail nutrients. Studies show that biotin supplementation can improve nail thickness and strength in brittle nails. Good sources include egg yolks, nuts, legumes, whole grains, and liver. Biotin is water-soluble and cannot be overdosed – excess is excreted. Typical doses in studies are 2.5 mg daily.

Iron is essential for many bodily functions, including nail growth. Iron deficiency is one of the most common causes of brittle, concave (spoon-shaped) nails. Good sources include red meat, legumes, dark green leafy vegetables, and fortified grain products. Absorption is improved with vitamin C.

Zinc supports keratin production and the immune system. A deficiency can lead to white spots on the nails, slower growth, and brittle nails. Good sources include meat, seafood, pumpkin seeds, nuts, and legumes.

Protein provides the amino acids for keratin, the main component of nails. Protein deficiency can lead to weak, brittle nails and slowed growth. Good sources include meat, fish, eggs, dairy products, legumes, and tofu.

Omega-3 fatty acids support nail hydration and can counteract brittle nails. Fatty fish, flaxseeds, and walnuts are good sources.

Vitamin C is important for collagen production and indirectly supports nail health. It also improves iron absorption.

Various nail changes can indicate different causes. Here's an overview – but keep in mind: not every change is pathological, and self-diagnosis is no substitute for a medical examination.

Brittle, splitting nails (onychorrhexis) are the most common nail problem. Causes can include: frequent contact with water and chemicals, biotin deficiency, iron deficiency, thyroid disorders, aging, or simply genetics. Treatment: Protect from moisture (gloves), eat a biotin-rich diet, and consider trying a biotin supplement.

Soft, thin nails can indicate protein deficiency, iron deficiency, or over-moisturization. Nails that are constantly in water become soft. Some medications can also affect nail structure.

Ridges in the nail: Longitudinal ridges are usually harmless and increase with age – like wrinkles on the skin. Transverse ridges (Beau's lines) are caused by a temporary disruption of nail growth and can indicate serious illness, high fever, chemotherapy, or severe stress at a particular time.

White spots (leukonychia) usually result from minor injuries to the nail matrix and are harmless. They grow out. The myth that they indicate a calcium deficiency is false – a zinc deficiency is more likely to be the cause.

Yellowish nails can be caused by nail polish (discoloration), fungal infection, smoking, psoriasis, or, rarely, by systemic diseases. Persistent yellowing should be investigated.

Spoon-shaped nails (koilonychia) – concave nails that could retain water – are a classic sign of iron deficiency (but can also have other causes).

Nail infections are common and can be persistent. Early detection and treatment improve the prognosis.

Nail fungus (onychomycosis) is a fungal infection of the nail that can cause discoloration (yellowish, brownish, whitish), thickening, brittleness, and separation from the nail bed. Toenails are more commonly affected than fingernails. Risk factors include moist environments (swimming pools, athletic shoes), circulatory disorders, diabetes, advanced age, and a weakened immune system.

Treatment requires patience: Topical antifungals (lacquers, creams) can help in mild cases, but require months of consistent application. In advanced cases, systemic antifungals (tablets) are often necessary. The nail must grow out completely (six to twelve months for toenails) before the result is visible.

Prevention: Keep feet dry, wear breathable shoes and socks, wear flip-flops or shower shoes in public areas (swimming pools, saunas), do not share nail clippers, treat early at the first signs.

Bacterial infections (paronychia) usually affect the cuticle and nail fold. Redness, swelling, pain, and possibly pus are typical symptoms. Causes are often minor injuries (from nail biting, manicures) or constant contact with water. Mild cases can be treated with antiseptic soaks; if an abscess forms or the condition worsens, a doctor should be consulted.

Viral warts can also appear under or next to the nails and affect nail growth. They require dermatological treatment.

In cases of persistent nail problems without an obvious external cause, a blood test may be useful to identify deficiencies or diseases.

Iron status: Ferritin (iron storage) is the most important value. Normal hemoglobin levels do not rule out iron deficiency – ferritin can be low long before blood cell production is affected. Optimal ferritin levels are above 50-70 ng/ml. Lower levels can already manifest as nail and hair problems.

Zinc: Serum zinc levels can be measured, but the results are not always conclusive. In cases of typical symptoms (white spots on nails, frequent infections, slow wound healing), a trial of treatment may be worthwhile.

Thyroid function: Both hyperthyroidism and hypothyroidism can affect the nails. Hypothyroidism often leads to brittle, dry nails and slowed growth. TSH, free T3, and free T4 levels should be checked.

Vitamin D: A link between vitamin D deficiency and nail problems is being discussed. Since vitamin D deficiency is common anyway and has many other effects, testing is advisable.

Protein status: If protein deficiency is suspected (vegetarian/vegan diet, eating disorders, chronic diseases), total protein and albumin can be determined.

Biotin levels are not usually measured routinely in the blood. A trial of biotin supplementation is often more practical than a test.

The DoctorBox metabolism check offers a comprehensive analysis of important blood values ​​that are also relevant for nail health – conveniently performed from home.

Besides diet, there are many practical measures that can support nail health.

Keep nails moisturized: They can dry out and become brittle. Apply a nourishing hand cream or nail oil after washing your hands and before going to bed. Don't forget to care for your cuticles – they protect the delicate nail matrix.

Protect yourself from chemicals: Wear gloves when cleaning, washing dishes, and working with chemicals. Even frequent contact with water alone softens nails and can lead to brittleness.

Gentle nail care: Don't cut nails too short – this can promote ingrown nails. File instead of cutting already brittle nails, and always file in one direction (not back and forth). Don't cut the cuticles, but gently push them back. Nail hardeners can help in the short term, but sometimes make nails more brittle in the long run.

Nail polish and remover: Occasional use of nail polish is fine, but continuous application without breaks can dry out your nails. Acetone-free nail polish removers are gentler. Leave time between manicures to allow your nails to 'breathe'.

Avoid biting or pulling your nails: This damages the nail plate and can lead to infections. For nervous nail biting, behavioral therapy or bitter-tasting nail polish can help.

Proper manicure technique: For gel or acrylic nails, choose experienced professionals. Removal should be gentle (soaking), not by scraping. Allow regular breaks between artificial nails.

The market for 'nail vitamins' and 'beauty supplements' is huge. But what is effective and what is just marketing?

Biotin has the strongest evidence for improving brittle nails. Several studies show improvements with 2.5 mg daily over several months. Side effects are not expected at this dose (although high doses of biotin can distort certain lab results – inform your doctor before any blood tests). A trial of three to six months is recommended for brittle nails.

Iron should only be supplemented if a deficiency has been diagnosed, as excessive doses can be harmful. If ferritin levels are low, iron supplementation can significantly improve nail health – but get tested first.

Zinc can help with deficiency symptoms. Doses of 15-30 mg daily are common. Caution is advised with long-term high intake – this can impair copper absorption.

Collagen supplements are heavily advertised. Research on their use for nails is limited, but some studies show improvements in nail brittleness and growth with collagen peptides. The mechanism is unclear, as collagen is digested and not directly incorporated into the body. Trying them won't hurt, but expectations should be realistic.

Silica (silicon) is traditionally recommended for nails and hair. The scientific evidence is weak. It won't do any harm, but don't expect miracles.

Combination products for 'skin, hair, and nails' often contain a little bit of everything. The dosages are sometimes too low to be effective. Targeted supplementation of individual nutrients in cases of proven deficiency or specific problem is often more sensible.

Most nail problems are harmless and due to external influences or minor deficiencies. However, some changes should be checked by a doctor.

Dark streaks or discoloration under the nail can be harmless (especially in people with darker skin), but they can also indicate melanoma. A new dark streak that changes or widens should be evaluated by a dermatologist – especially in fair-skinned individuals.

Detachment of the nail from the nail bed (onycholysis) without obvious injury may indicate fungal infection, psoriasis, thyroid problems, or other diseases.

Significant thickening or deformation of the nails, especially if only individual nails are affected, should be investigated – fungal infections, psoriasis, or other causes are possible.

Clubbed nails (strongly curved, fingers like drumsticks) can indicate heart or lung diseases and should definitely be examined by a doctor.

Inflamed, painful cuticles with pus may require antibiotic treatment.

Sudden changes in several nails at the same time can indicate systemic diseases.

The appropriate specialist for nail diseases is usually a dermatologist (skin doctor). If nail fungus is suspected, the general practitioner can also provide initial treatment. If systemic causes (thyroid, iron deficiency) are suspected, the general practitioner or internist is responsible.

How long does it take for dietary changes to become visible on the nails?

Since nails grow slowly (about three to four millimeters per month for fingernails) and the nail plate itself is not living, it takes several months for improvements to become visible. A fingernail takes about six months to completely regenerate. Realistically, you should plan for three to six months of consistent dietary changes or supplementation before evaluating results.

Do nail hardeners really help?

Nail hardeners containing formaldehyde or similar substances can make nails appear stronger in the short term. However, in the long run, they can dry out nails and make them even more brittle. If you use nail hardeners, take regular breaks. Better long-term strategies come from within: good nutrition, sufficient moisture, and protection from external influences.

What do white spots on the nails mean?

White spots (leukonychia) usually result from minor bumps or injuries to the nail matrix – often so slight that they go unnoticed. They are harmless and grow out. The myth that they indicate a calcium deficiency is untrue. While zinc deficiency could theoretically play a role, in most cases they are simply caused by mechanical microtrauma.

Is biotin really that important for nails?

Biotin is the most studied nutrient for brittle nails, and the evidence is relatively good. Several studies show improvements with doses of 2.5 mg daily. Biotin is water-soluble, cannot be overdosed, and has few side effects. A three-month trial is worthwhile for brittle nails. However, if there is no biotin deficiency, more biotin will not help.

Why do my toenails grow so slowly?

Toenails grow physiologically slower than fingernails – about one millimeter per month instead of three to four. This is due to lower blood flow and less stimulation. Growth slows down further with age. A complete toenail takes twelve to eighteen months to regenerate. This also explains why toenail fungus is so difficult to treat.

Can I treat nail fungus myself?

In very early stages (small discoloration at the edge of the nail), over-the-counter antifungal nail polishes can help. However, treatment must be continued consistently for several months. For more extensive infections (more than half the nail) or if the nail matrix is ​​affected, prescription tablets are often necessary. Consult a doctor if home remedies are ineffective after two to three months or if multiple nails are affected.

Does gel manicure damage the nails?

Gel nails themselves aren't necessarily harmful, but the process can be problematic: UV lamps mean UV exposure (apply sunscreen to your hands beforehand). Removing them by scraping or soaking them for too short a time damages the nail plate. Without breaks between treatments, the nails can't regenerate. Occasional gel manicures at a reputable salon are fine, but take regular breaks between treatments.

My nails have all become ridged after an illness – is that normal?

Yes, transverse ridges (Beau lines) appear when nail growth has been temporarily disrupted – by high fever, serious illness, significant stress, or chemotherapy. They essentially indicate the time of the disruption. The ridges grow out with the nail and disappear after a few months. If you know when you were ill, you can even pinpoint the exact time based on the position of the ridge.

Do the nails indicate a protein deficiency?

Yes, since nails consist mainly of the protein keratin, a protein deficiency can lead to soft, thin, and slow-growing nails. However, this is rare in wealthy countries – even vegetarian and vegan diets usually provide enough protein. Protein deficiency can occur in cases of eating disorders, extreme diets, or certain illnesses.

Why are some nails curved or spoon-shaped?

Slightly curved nails can be hereditary. Severely concave (spoon-shaped) nails (koilonychia) are a classic sign of iron deficiency. If the nails are so concave that they could retain water, iron levels should be checked. Other possible causes include thyroid problems, constant contact with solvents, or, very rarely, congenital disorders.

Does calcium help strengthen nails?

No, that's a common myth. Nails are made of keratin (a protein), not calcium like bones. Calcium supplementation won't improve brittle nails. The more important nutrients for nails are biotin, iron, zinc, and high-quality protein. Calcium is certainly important for overall health, but not primarily for nails.