Nail Treatment — What Actually Works on Brittle Nails? Facts vs Myths

Nail treatments promise miracles: harder, thicker, glossy nails in two weeks. The reality is more complicated. To understand what might actually work and what is pure marketing fiction, you first need to understand what you're dealing with — because the nail plate is dead tissue.

Anatomy of the problem: the nail is dead keratin

The visible part of the nail (the plate) consists of 80–90 layers of compressed, keratinized cells (corneocytes) made of hard alpha keratin. These cells are already dead — they have no nucleus, don't metabolize and don't "nourish themselves." Any structural change can only take place in the nail matrix — the hidden growth zone beneath the skin at the base of the nail.

This is a fundamental point, because it means that:

• Ingredients applied onto the plate can at most coat, seal or temporarily harden it — but they won't change its structure.
• To genuinely strengthen nails, you have to influence the matrix — and that requires working from within (diet, supplementation) or long-term care of the growth area.

Formaldehyde — the hardening paradox

Formaldehyde (and its derivatives, such as formalin) was the gold standard in hardening treatments for decades. The mechanism is simple: formaldehyde forms cross-links between keratin chains, making the plate harder and more resistant to bending.

The problem? It works — but only in the short term, and at the cost of the nail's long-term health:

• The first 2–4 weeks: nails are harder and break less often.
• After 4–8 weeks of continuous use: excessive cross-linking of keratin makes the plate brittle as glass. Instead of flexing, it cracks. Paradoxically, a hardening treatment leads to greater brittleness.
• On top of that: formaldehyde is a potent contact allergen and a carcinogen (IARC Group 1). It can cause onycholysis — separation of the plate from the nail bed.

EU regulations allow up to 2.2% formaldehyde in nail-hardening products (with an appropriate warning on the label), but many dermatologists advise against long-term use.

The calcium myth — one of the most persistent in cosmetology

"Nails break because they lack calcium" — a sentence repeated for generations, but one that has no scientific basis. Analysis of the mineral composition of nails shows that calcium accounts for just 0.1% of the plate's mass (vs 10% sulphur, which is responsible for the disulphide bonds in keratin).

The Sirck and King study from 1969, cited many times in the dermatological literature, found no correlation between calcium concentration in nails and their hardness or brittleness. Brittle nails are a problem of hydration and keratin bonds, not mineralization.

Treatments "with calcium" exploit this myth — calcium pantothenate on the INCI list sounds convincing, but it is simply a form of vitamin B5, not a calcium that strengthens the structure.

Biotin — the only supplement with solid evidence

Biotin (vitamin B7, formerly H) is the only orally taken substance for which controlled studies confirm an effect on nail thickness and hardness:

• The Floersheim study (1989): a dose of 2.5 mg/day for 6–15 months increased plate thickness by 25% in patients with brittle nail syndrome. This study is a milestone in the field.
• The Hochman study (1993): 63% of participants reported improvement after supplementing with 2.5 mg of biotin daily.
• The Iorizzo meta-review (2022) in the Journal of Dermatological Treatment: confirmed that biotin at 2.5–5 mg/day is effective, but requires a minimum of 3–6 months of regular use.

Why so long? Because biotin acts on the matrix — the growth zone. A nail grows about 3 mm per month, so the strengthened keratin literally has to "grow out" from the base to the free edge.

Hydrolyzed keratin — intelligent surface coverage

Hydrolyzed keratin consists of keratin protein fragments broken down into smaller peptides (1–10 kDa), which can penetrate the upper layers of the plate and fill in micro-damage. The mechanism resembles how a protein mask works on hair:

• Keratin peptides settle into irregularities on the plate's surface.
• They form a reinforcing layer that reduces susceptibility to peeling.
• The effect is temporary — it requires regular reapplication — but safe, with no risk of over-hardening.

It is one of the few surface ingredients with a logical biochemical rationale. Check whether your treatment contains it — search for "Hydrolyzed Keratin" in the PurScore ingredient database.

What else makes sense?

• Cyanoacrylate (in "silk"-type treatments): forms a thin, flexible film that mechanically protects the plate. It doesn't strengthen the keratin, but it prevents further cracking.
• Low-molecular-weight hyaluronic acid: draws water to the surface of the plate, improving flexibility. Nails containing 16–18% water are optimal; below 16% they become brittle.
• Panthenol (provitamin B5): a humectant that improves hydration of the skin around the nail, but doesn't penetrate the plate itself to any significant degree.

A strategy for brittle nails

1. From within: biotin 2.5 mg/day for at least 6 months (after consulting a doctor — biotin interferes with TSH test results).
2. On the surface: a treatment with hydrolyzed keratin, free of formaldehyde.
3. Every day: cuticle oil (jojoba + vitamin E) — well-moisturized areas around the nail support healthy growth.
4. Avoid: formaldehyde treatments for longer than 2–3 weeks, excessive contact with water and detergents, and filing wet nails.

Learn how to read the composition of nail treatments and spot formaldehyde substitutes in our guide to the INCI list.