Biotin (Vitamin B8): Hair, Nails, Benefits, Risks and Dosage (The Complete 2026 Guide)

★ Patented keratin, biotin and zinc

Keratin • Biotin

Three complementary levers for hair fiber and nails: Cynatine® HNS, a solubilized keratin that was the subject of a randomized trial, zinc which contributes to the maintenance of normal hair and nails, and biotin at 100% of the reference value, without unnecessary overdose.

Cynatine® HNS 500 mg Biotin 100% NRV Zinc 1 capsule per day

Discover Keratin • Biotin →

1. Biotin, vitamin B8, B7, H: three names, one vitamin

The story of biotin begins with an absurd diet. In the 1920s, researchers fed rats almost exclusively raw egg white and watched them lose their hair, develop dermatitis and nervous disorders; they call this condition "egg white disease." A factor present in liver and yeast cures it: they name it vitamin H, from the German Haar und Haut, hair and skin, because these are the organs that suffer first. It wasn't until 1940 that the mechanism was understood: raw egg white contains a protein, calledavidin, which binds to biotin with a force that has almost no equivalent in biology and prevents it from being absorbed. Cooking denatures avidin and resolves the problem. This extraordinary binding, the strongest known between a protein and a small molecule, goes far beyond anecdote: it is what laboratories use in hundreds of blood tests, and this is why excess biotin distorts them (section 9).

The nomenclature subsequently diverged. French tradition and part of Europe classified it as vitamin B8 ; English-speaking countries and international scientific literature say vitamin B7 ; and the name vitamin H survives on some packaging. When you read "B8" on a French supplement and "B7" on an American website, it is the same molecule, measured in the same unit, the microgram.

Chemically, biotin is a small sulfur-containing molecule with two rings, extended by a carbon chain that allows it to attach to its enzymes. It serves as a cofactor for five carboxylases, enzymes that transport carbon dioxide from one molecule to another. This role as a CO₂ shuttle places it at metabolic crossroads: the manufacture of fatty acids, the production of glucose from lactate or amino acids when sugar reserves drop, the breakdown of leucine and certain fatty acids with an odd number of carbons. The body recycles it thanks to an enzyme, called biotinidase, which detaches it from worn-out proteins for reuse; when this enzyme is missing, due to genetic mutation, deficiency develops despite normal intake (section 5).

2. What is biotin for? Health claims authorized by the EFSA

The biological role of biotin passes almost entirely through its five carboxylases. Theacetyl-CoA carboxylase initiates the synthesis of fatty acids, which make up the membranes of all cells and the lipid film that protects the skin and scalp. The pyruvate carboxylase restarts glucose production between meals and during exercise. The propionyl-CoA carboxylase and the 3-methylcrotonyl-CoA carboxylase break down certain amino acids and fatty acids; when they slow down, organic acids accumulate in the urine, and their measurement is what now allows for precise assessment of biotin status. For about twenty years, it has also been known that biotin binds to histones, the proteins around which DNA wraps, and participates in regulating the expression of certain genes; the practical importance of this role remains debated.

European regulation No. 432/2012 authorizes seven claims for biotin, provided that the product provides at least 15% of the NRV (7.5 micrograms) per serving. Biotin contributes:

• to normal energy metabolism ;
• to normal functioning of the nervous system ;
• to normal metabolism of macronutrients ;
• to normal psychological functions ;
• to maintenance of normal hair ;
• to maintenance of normal skin ;
• to maintenance of normal mucous membranes.

The last three are the ones that sell, and they deserve to be read word for word. The EFSA granted them because biotin deficiency causes hair loss and dermatitis, and correcting the deficiency makes them disappear: biotin is therefore necessary for normal hair and skin. It granted no claims regarding hair growth their density, their thickness or reduction of hair loss, because no study demonstrates this in a person without deficiency. A product that promises "thicker hair" or "accelerated regrowth" thanks to biotin goes beyond the authorized framework. We return to this in detail in section 6, because that is the entire question.

3. How much biotin per day? Needs and absence of limits

Two characteristics distinguish biotin from other B vitamins. The first is that its requirements are expressed as "adequate intake" rather than "population reference intake": data are lacking to establish a precise average requirement, and the value of 40 micrograms corresponds to what healthy populations consume, with no sign of deficiency. Colon bacteria also produce an unknown quantity, part of which is absorbed: this is one reason why pure dietary deficiency is so rare.

The second characteristic is theabsence of an upper safety limit. Neither the EFSA nor the American Institute of Medicine has established one, because no toxicity has been reported, even in clinical trials at 300 milligrams per day—7,500 times the requirement—conducted for over a year (section 10). Excess biotin is simply eliminated in the urine. It is this absence of a limit that has enabled the emergence of supplements at 5,000 or 10,000 micrograms, proudly displaying "10,000% of the NRV." This figure should be read for what it is: a dose that nothing prohibits, and that nothing justifies either, since no study has shown that beyond requirements, more biotin produces more hair. And while excess is not toxic to the body, it is toxic to your lab results, which led the American drug agency to issue two alerts in 2017 and 2019.

4. Biotin-rich foods (and the raw egg trap)

An average French adult consumes approximately 30 to 70 micrograms of biotin per day according to surveys, thus around or above the adequate intake level. The vitamin is relatively stable to heat but water-soluble: some passes into cooking water. Its bioavailability varies depending on whether it is free or bound to food proteins, and intestinal biotinidase must release it before absorption, which occurs via a specific transporter (SMVT) also shared by pantothenic acid (vitamin B5) and lipoic acid, a detail that will be relevant regarding acne (section 11).

The raw egg trap deserves mention, as it has its followers among athletes and homemade recipe enthusiasts. A whole raw egg provides no biotin: its white contains enough avidin to block that of the yolk and some from the rest of the meal. A raw egg from time to time poses no problem; two to six raw whites daily for months have produced documented deficiencies, with hair loss and dermatitis. The solution is simple: cook the white, even lightly. A soft-boiled or fried egg is enough to denature the avidin and restore the biotin from the yolk.

5. Biotin deficiency: symptoms, causes, at-risk populations

Who lacks biotin? The first cause, and the most serious, is genetic: biotinidase deficiency, a rare disease (approximately one birth per 60,000 for the severe form) in which the recycling enzyme is deficient. The child is born normal, then develops within weeks or months seizures, eczema, hair loss, hypotonia and deafness; a few milligrams of biotin daily, for life, prevents all of this. This is why most countries have included it in newborn screening, and it is one of the rare childhood epilepsies treatable with a vitamin (Tabarki, Arch Pediatr, 2013; Küry, Eur J Hum Genet, 2015). Holocarboxylase synthetase deficiency, the enzyme that binds biotin to its carboxylases, is even rarer and is treated in the same way.

In adults, acquired deficiencies arise from specific situations: long-term antiepileptic drugs (carbamazepine, phenytoin, phenobarbital, valproic acid), which impair absorption and accelerate biotin degradation;alcoholism, which inhibits its intestinal transporter; prolonged parenteral nutrition without vitamin supplementation, a historical cause of severe deficiencies before solutions systematically contained it; extensive digestive diseases and bariatric surgery; and regular consumption of raw egg white. Long-term broad-spectrum antibiotics, by depleting the flora that produces biotin, can contribute to this.

Pregnancy is the most interesting case because it concerns a large, asymptomatic population. Research by Donald Mock's team showed that in the third trimester, approximately one in two women present urinary markers of marginal deficiency with no clinical signs, likely because biotin is broken down more quickly and consumed by the fetus. In animals, deficiency at this level is teratogenic (cleft palate, limb malformations); in women, the link is not demonstrated but has never been ruled out. This is not a reason to take massive doses, but rather an argument for prenatal formulas to provide biotin at nutritional doses, alongside est le cas le plus intéressant parce qu'il concerne une population large et sans symptôme. Les travaux de l'équipe de Donald Mock ont montré qu'au troisième trimestre, une femme sur deux environ présente des marqueurs urinaires de carence marginale, sans aucun signe clinique, probablement parce que la biotine est dégradée plus vite et consommée par le fœtus. Chez l'animal, une carence de ce niveau est tératogène (fentes palatines, malformations des membres) ; chez la femme, le lien n'est pas démontré mais n'a jamais été écarté. Ce n'est pas une raison d'avaler des doses massives, plutôt un argument pour que les formules prénatales apportent la biotine à dose nutritionnelle, aux côtés de l'folic acid whose importance is established.

6. Does biotin really make hair grow?

This is the question everyone asks, and the honest answer comes down to one distinction. Biotin is necessary for hair: without it, follicles suffer, keratinization goes awry and hair falls out. But "necessary" does not mean "more is better." Once needs are met, the enzymes that depend on biotin are saturated, and the excess is excreted in the urine without having changed anything in the follicle. The reasoning is the same as for water and a plant: a plant lacking water greens up when watered; a well-watered plant doesn't grow faster if you double the watering. The whole question is therefore whether you are deficient in biotin. And in adults eating normally, the answer is almost always no.

Eighteen cases over forty years of literature—that's what the evidence for biotin on hair amounts to. And all these patients had something: biotinidase deficiency, deficiency related to antiepileptic drugs, uncombable hair syndrome (a rare genetic condition affecting the hair shaft), brittle nail syndrome. To date, there exists no randomized, placebo-controlled trial showing that biotin alone increases density, diameter, growth rate or reduces shedding in people without deficiency. The few positive trials "with biotin" involve complex formulas (marine proteins, zinc, vitamin C, botanicals) where it is just one ingredient among ten, and whose effects are not attributable to it.

Why are so many people convinced it works? Because three mechanisms combine, none involving dishonesty. The first istelogen effluvium, reactive shedding: after childbirth, fever, dieting, or trauma, an abnormal proportion of hairs enters the resting phase and falls out two to three months later, then regrowth occurs naturally over three to six months. If you start biotin at the peak of shedding, you stop it when natural regrowth begins and credit biotin with the result. The second is unrecognized deficiency : a person on antiepileptic drugs, a heavy consumer of raw egg whites, a pregnant woman in late pregnancy may have marginal status and genuinely respond. The third is the hair cycle itself : because any change takes three to six months to become visible, any natural fluctuation in shedding (seasonal, particularly) can be attributed to the supplement started in the meantime. Controlled trials exist precisely to sort all this out, and for biotin alone, they are lacking.

What this means in practice: if your hair is falling out, biotin is not the first question to ask. Frequent and correctable causes are iron (low ferritin, very common in menstruating women), the thyroid, vitamin D, zinc, a telogen effluvium to let pass, and in both men and women theandrogenetic alopecia, hormonal, which only specific treatments slow down. Our article on the 8 proven actives against hair loss details what trials actually support. Biotin has its place as a component of complete nutritional intake, not as a treatment.

7. Biotin and brittle nails: the only solid signal

The story of biotin and nails begins in the stables. In the 1980s, veterinarians observed that horses with cracked and brittle hooves showed marked improvement in horn quality on high-dose biotin, a result confirmed by controlled trials in animals. The hoof and nail are made of the same hard keratin, and dermatologists had the idea to transpose this. A Swiss study then measured, by electron microscopy, a 25% increase in the thickness of the nail plate in patients with brittle nails after several months of biotin, with a reduction in splitting. A New York team subsequently published the most-cited series.

We must be realistic about the level of evidence: a retrospective series without control group, an imaging study on about twenty patients, no randomized trial in thirty years. But the signal is consistent with the biology (biotin is involved in the synthesis of lipids that cement keratin cells) and with animal data, and it is on this that the recommendation rests, still common among dermatologists, to propose 2.5 milligrams per day for six months in the brittle nail syndrome, after having ruled out iron deficiency, hypothyroidism, psoriasis or fungal infection.

In practice, brittle nails respond first to simple measures: limit prolonged contact with water and detergents (gloves), avoid harsh solvents and repeated gel nails, hydrate the nail plate and cuticles, keep them short. A supplementation combining biotin at a moderate dose, zinc (which also carries the claim "contributes to the maintenance of normal nails") and assimilable keratin is a reasonable option, to be judged after four to six months, the time it takes for a fingernail to completely renew itself.

8. Keratin, zinc, biotin: why combine them

A hair is 95% keratin, a protein rich in cysteine whose sulfur bonds provide strength. To make it, the follicle needs sulfur-containing amino acids (cysteine, methionine), energy, and a battery of cofactors: zinc for enzymes of cell division, biotin for scalp lipid metabolism, B vitamins for energy production, iron for bulb oxygenation. A coherent formula does not seek to maximize one of them but to ensure that none is lacking.

<<<28>>> Keratin supplementation kératine en complément has long been a dead end: native keratin is insoluble and indigestible, and standard hydrolysates are broken into fragments that have little that is specific. Cynatine® HNS is a solubilized keratin derived from sheep's wool by a process that preserves cysteine-rich peptides and makes them absorbable; it is one of the very few to have been tested in a randomized placebo-controlled trial.

This trial calls for an honest reading. It is small (25 women per group), short (90 days, barely enough time for one renewal cycle), it was funded and partly conducted by the ingredient manufacturer, and the formula tested also contained zinc and vitamins, so that the effect cannot be attributed to keratin alone. It has not been reproduced by an independent team. This is an encouraging signal, not definitive proof, and it places Cynatine HNS a notch above keratins with no data at all, which is already something in a market where most "hair keratins" have never been tested on anyone.

<<<38>>> Zinc zinc is the third pillar, and the best established of the three nutritionally: it carries the claims "contributes to the maintenance of normal hair, normal nails and normal skin," its deficiency causes documented hair loss, and low status is common in women, vegetarians and the elderly. As with biotin, correcting it is useful, exceeding it is not, and excess zinc long-term (beyond 25 mg per day) impairs copper absorption. Our Keratin • Biotin combines these three mechanisms in one capsule: 500 mg of Cynatine HNS, zinc, and biotin at 50 micrograms, or 100% of the reference value. This last figure is not a weakness: it's the dose that covers needs, without the overdose that would skew your blood work.

9. The real danger: biotin skews your blood tests

Here is the paradox: biotin is not toxic, and yet it can harm you seriously. The reason lies in the avidin from section 1, or rather in its bacterial cousin, streptavidin. Because the biotin-streptavidin bond is the strongest and most specific that biology knows, blood test manufacturers use it as universal glue: they attach biotin to test antibodies and streptavidin to the support, and the assay builds on this anchor. The system is elegant, it equips the majority of laboratory analyzers, and it has a weak point: if the patient's blood already contains a lot of biotin, it occupies the streptavidin sites and the test malfunctions.

The consequences are not theoretical. The American drug agency (FDA) published a first alert in November 2017 after receiving a report of a patient who died of a heart attack whose troponin, the blood marker of heart damage, had come back falsely normal because of the biotin he was taking. It renewed it in 2019, finding that some troponin tests remained sensitive. Since then, the literature has accumulated cases of false hyperthyroidism wrongly treated, of blood pregnancy tests falsely negative, of vitamin D, of testosterone, of cortisol, of ferritin, of PSA or aberrant tumor markers . In high-dose biotin trials in patients with multiple sclerosis, 4.7% had falsified laboratory analysis, versus none under placebo, despite precautions taken (Espiritu, 2021).

Starting at what dose? Biotin has a short half-life (a few hours) and interference depends on blood concentration at the time of sampling. The doses in "hair" supplements (5,000 to 10,000 micrograms) produce peaks more than sufficient to skew sensitive tests for several hours, and some reagent manufacturers estimate that daily intake of 1,000 micrograms can already pose a problem depending on sampling timing. At 50 or 300 micrograms, the doses in a B-complex or our formula, the risk is considered negligible with most current tests, but the precautionary principle applies to everyone.

10. High-dose biotin and multiple sclerosis: hope then failure

This story deserves to be told, because it circulated through forums and patients continue to buy high-dose biotin powder based on it. The original idea was appealing: in progressive multiple sclerosis, demyelinated neurons lack energy, and biotin-dependent carboxylases are involved in both energy production and myelin fatty acid synthesis. A French team therefore tested pharmaceutical-grade biotin, MD1003, at 300 milligrams per day, or 7,500 times the adequate intake.

The meta-analysis that followed, pooling three randomized trials and 889 patients, settles it: evidence of disability improvement is insufficient and of low certainty, a modest signal persists on walking speed, tolerance is identical to placebo, and the only high certainty concern is laboratory interference, observed in 4.7% of treated patients and no controls (Espiritu, Mult Scler Relat Disord, 2021). The manufacturer withdrew its authorization request. A pilot trial in amyotrophic lateral sclerosis also showed no efficacy.

Two lessons for the reader without multiple sclerosis. First: at 300 milligrams per day for over a year, biotin was tolerated as well as placebo, which confirms its absence of direct toxicity and explains why no safety limit exists. Second: this same trial is the one that best documented falsified analyses. In other words, biotin won't harm you in itself, but it can lead your doctor to make wrong decisions. What neurologists learned to manage in a controlled trial, an individual buying biotin powder online does not manage.

11. Weight gain, acne, constipation: real and imaginary side effects

A word on pregnancy and breastfeeding : biotin at nutritional dose is necessary and present in all prenatal formulas. Very high doses, on the other hand, are not recommended as a precaution: animal toxicity data at these levels are limited, and teratogenicity has been observed in one species with MD1003. This is no reason to worry about a B complex at 300 micrograms, but it is a reason not to take 10,000 micrograms "for hair" while expecting a child.

12. When and how to take it, interactions

Biotin has no particular chronobiology: it is absorbed well on an empty stomach as well as with a meal, and nothing justifies splitting doses. Evening or morning, it doesn't matter; what matters is consistency, because what counts unfolds over months. Hair grows approximately one centimeter per month and a fingernail renews in four to six months (nine to twelve for a toenail): a change in fiber or nail plate quality only becomes visible as the newly formed part replaces the old. A first assessment at three months, judgment at six, photos under the same lighting: it's the only way not to fool yourself, either way.

Precautions Biotin at nutritional dose is suitable for everyone, including during pregnancy and breastfeeding. Very high doses are not recommended during pregnancy and, for everyone, before blood work or scheduled hospitalization. Respect the indicated daily dose, keep supplements out of children's reach, and remember that a supplement cannot replace a varied and balanced diet or a healthy lifestyle. If you experience hair loss lasting more than six months, patchy alopecia, facial dermatitis, or deformed nails, consult a professional: these are symptoms, not cosmetic concerns.

13. Choosing well: dose, form, combination

The biotin market operates on a simple equation: the highest dose makes the best argument, since no limit prohibits it and "10,000% of NRV" impresses. Our position is the opposite, and it stems from everything above: the dose that makes sense is one that covers needs, with a reasonable margin, combined with the other nutrients that hair and nails truly depend on. A few criteria for reading a label:

• The daily biotin dose : 50 to a few hundred micrograms amply cover needs, even increased ones. Beyond 1,000 micrograms, you're paying for an overdose with no proven benefit and you enter the zone where blood test results can be skewed.
• The partner nutrients : zinc (between 5 and 15 mg), possibly a solubilized keratin with published data, selenium or copper at moderate doses; for general intake, the other B vitamins.
• The form : D-biotin is the only active form and the only one used in supplements; no "superior form" exists, be wary of arguments along these lines.
• The format : gummies often contain 2 to 4 g of sugar and flavorings for just a few micrograms of vitamin; a capsule does the same job without all that.
• The claims : "accelerated growth," "thicker hair," "stops hair loss" are not authorized claims for biotin. A serious product speaks of contributing to the maintenance of normal hair and nails.

Frequently asked questions about biotin

Learn more