Taking keratin to have beautiful hair has something intuitive about it, since hair is made of keratin, and something suspicious about it, because the body doesn't simply glue what you give it where you want it. The skepticism is legitimate, and it even has a solid basis: ordinary keratin is indigestible. A feather, a hair, a nail pass through the digestive tract without being broken down.
So the question is not "does keratin work," but " which keratin ". This article explains why the raw form is useless, what a solubilized keratin changes, then presents the two randomized double-blind trials that measured the effect of these absorbable forms on hair, nails and skin, with their figures, their limitations and their affiliations. Then what keratin does, what it doesn't do, and how to read a label.
The condition. Raw keratin is locked by sulfur bridges that digestion cannot open: swallowed as-is, it's useless. A solubilized or hydrolyzed keratin is absorbable, and that's what was tested. The evidence. Two randomized double-blind trials of 90 days : Cynatine HNS at 500 mg in 50 women, hair loss, growth, strength, shine and nails significantly improved ; a keratin hydrolysate at 500 and 1,000 mg, skin, hair and nails all improved versus placebo.
What it does. Improves growing hair and nails, in three months. What it does not do. Revive a hair follicle shut down by established baldness. The label. The word "keratin" alone says nothing; "solubilized," "hydrolyzed," or a patented name with published trials tells you what you're buying. The benchmark: 500 mg per day, three months, with zinc and biotin.
What keratin is, and why raw keratin is useless
<<<34>>> Keratin kératine is the structural protein of hair, nails, and the superficial layer of skin. Hair is made of it at 95%. What distinguishes it from other proteins is its richness in cysteine, a sulfur-containing amino acid: the sulfur atoms of two neighboring cysteines bond to form a disulfide bridge, and these bridges link the keratin chains together like the rungs of a ladder. This is what makes hair resistant, nails hard, horn impermeable.
It is also what makes it indigestible. Digestive enzymes break down proteins into amino acids by cutting the main chain; they cannot open the sulfur bridges that lock it. A feather, a hair, a nail pass through the stomach and intestine almost completely intact. Cats regurgitate their hairballs for this exact reason.
A capsule of keratin raw, ground feather or horn powder, is a protein that the body cannot use. It is cheap, it is legitimately called keratin, and it is useless. This is the source of skepticism about keratin capsules, and this skepticism is justified for this form.
The whole question is whether the keratin in the product has been treated to become absorbable. Clinical trials focused on these treated forms, and on them alone.
What solubilized keratin changes
Making keratin absorbable consists of opening the disulfide bonds without destroying the amino acids they protect, and in particular without oxidizing cysteine, which is the most valuable building block for the follicle. Two families of processes achieve this.
| Form | Process | What happens to the follicle | Clinical trial |
|---|---|---|---|
| Raw keratin | Grinding of feathers, horns, hooves | Nothing : undigested, unabsorbed | None |
| Solubilized keratin, Cynatine HNS | Patented process on sheep's wool, bridges opened, peptide structure preserved, active cysteine | Peptides and sulfur amino acids absorbable | Randomized, double-blind, 50 women, 90 days |
| Keratin hydrolysate | Advanced hydrolysis of feathers, up to over 80% free amino acids | Free amino acids directly absorbable | Randomized, double-blind, three groups, 90 days |
The two treated forms have one thing in common: they deliver to the follicle and nail matrix the sulfur amino acids they need to manufacture new fiber, at the moment they are manufacturing it. The difference between them lies in the degree of breakdown; trials show that both work.
The Cynatine HNS trial: 50 women, 90 days
A randomized, double-blind, placebo-controlled trial, published in The Scientific World Journal and registered under a public EudraCT number, included 50 women. Twenty-five received for 90 days two capsules per day containing 500 mg of Cynatine HNS with vitamins and minerals; twenty-five received two identical capsules of maltodextrin.
| Measured criterion | Result, keratin versus placebo |
|---|---|
| Hair loss | Statistically significant improvement |
| Growth | Statistically significant improvement |
| Fiber strength | Statistically significant improvement |
| Amino acid composition of hair | Improved: ingested keratin is found in the fiber |
| Shine | Improved |
| Nail strength | Significantly improved |
| Nail appearance | Significantly improved |
The authors conclude that Cynatine HNS is an effective supplement for improving hair and nails in 90 days or less. The most telling criterion is the amino acid composition of hair: if it changes under keratin, it means that the ingested keratin was indeed absorbed and incorporated into the new fiber, which directly addresses the question of bioavailability.
The hydrolysate trial: skin, hair, nails
A second randomized, double-blind, placebo-controlled, multicenter trial, published in 2024 in the Journal of Cosmetic Dermatology, tested a keratin hydrolysate feather, broken down to over 83% free amino acids, in women showing signs of aging. Three groups: 500 mg, 1,000 mg, or placebo, for 90 days.
| What was measured | Result at 90 days, versus placebo |
|---|---|
| Skin : roughness, wrinkles, deep hydration, elasticity, firmness, thickness | Significantly improved at both doses |
| Skin, hair and nail radiance | Significantly improved at both doses |
| Nail hardness | Significantly improved at both doses |
| Density and anisotropy of skin fibers | Improved from baseline, trend versus placebo |
| Self-assessment by participants | Positive responses in both keratin groups, not under placebo |
The authors conclude that 90 days of keratin hydrolysate improve the appearance of facial skin, hair and nails, and put forward an interesting idea: free amino acids act not only as building blocks, but also as signals for cells, what they call "aminobiotics".
Two different teams, two different keratins, solubilized wool and hydrolyzed feather, two countries, ten years apart, and the same result at 90 days on hair and nails. This is what elevates absorbable keratin from promising ingredient status to documented ingredient status. The second trial has authors affiliated with the manufacturer and testing laboratory, which we also note.
It also notes that the 1,000 mg dose did not perform clearly better than 500 mg: the benchmark of 500 mg per day holds in both trials.
What it does, what it doesn't do
| What solubilized keratin does | What it doesn't do |
|---|---|
| Reduces hair loss and improves growth of hair whose follicle is active | Revive a follicle shut down by established androgenetic alopecia |
| Strengthens new hair fiber: resistance, shine, composition | Repair hair fiber already grown, damaged by heat or coloring |
| Hardens nails and improves their appearance in 90 days | Treat nail fungus or nail psoriasis |
| Improves skin hydration, elasticity and shine | Replace sunscreen or dermatological treatment |
| Works in three months, the time it takes for new hair and nails to grow | Act in two weeks: hair grows one centimeter per month |
Keratin nourishes a follicle that produces. In seasonal hair loss, reactive or linked to a deficiency, the follicle is intact and restarts: this is the terrain for trials. In established androgenetic alopecia , receding temples, thinning at the crown for years, the follicles have miniaturized and shut down, and no amino acid will reactivate them. Keratin can improve the quality of remaining hair; it does not restore lost density, and this condition requires a dermatologist.
Reading a label: form, dose, cofactors
The form
It's the only criterion that truly matters. The word "keratin" alone says nothing: it can refer to indigestible raw powder. Look for "solubilized", "hydrolyzed", "hydrolysate", or a patented ingredient name like Cynatine HNS, which refers to an identifiable process and published trials. Price is a clue: solubilized keratin costs significantly more to produce than ground feather.
The dose
500 mg per day of solubilized keratin is the dose from the Cynatine trial and the low dose from the hydrolysate trial, where 1,000 mg did not perform clearly better. A capsule containing significantly less does not reproduce what was tested.
The cofactors
Both trials combined keratin with vitamins and minerals, and this is no accident. Keratin provides the building blocks ; the follicle needstools to assemble them.
- Zinc plays a role in the division of follicle cells, among the fastest-dividing in the body, and in keratinization enzymes. In 312 patients suffering from hair loss, all types combined, blood zinc was significantly lower than in controls, 84 versus 98 µg/dl, and the authors conclude that its metabolism plays a key role in hair loss.
- Biotin, vitamin B8, is the cofactor of enzymes that synthesize keratin. The reference review on vitamins and hair loss, notably signed by Antonella Tosti, recalls that its deficiency causes fine hair and hair loss, and that the benefit is clearest when intake is insufficient. Our biotin guide details dosages and limitations.
What to do practically
Frequently asked questions
Understanding
Keratin in capsules, does it work?
Yes, on one condition: that the keratin is solubilized or hydrolyzed, and therefore absorbable. Two randomized, double-blind, placebo-controlled trials lasting 90 days each measured this. The first, in 50 women taking Cynatine HNS at 500 mg, showed statistically significant improvements in hair loss, growth, strength and shine, and nail strength. The second, with a keratin hydrolysate at 500 or 1,000 mg, showed significant improvement in all skin, hair and nail parameters compared to placebo. Raw, untreated keratin would not produce these results because it is not digested.
What is keratin?
The structural protein of hair, nails and the superficial layer of skin. Hair is made of it 95%. Its distinctive feature is its richness in cysteine, a sulfur-containing amino acid whose bonds, called disulfide bonds, link the chains together and give hair and nails their strength. This structure makes it both resistant and, in its raw form, virtually indigestible.
Why is ordinary keratin indigestible?
Because of these same disulfide bonds. Digestive enzymes break down proteins into amino acids, but they cannot open the sulfur bonds that lock keratin. A feather, a hair or a nail passes through the digestive tract virtually intact: this is why cats regurgitate their hairballs. Swallowing raw keratin amounts to swallowing a protein that the body cannot use.
What is solubilized or bioavailable keratin?
Keratin industrially treated to open disulfide bonds without destroying amino acids, making it soluble, digestible and absorbable. Cynatine HNS is obtained from sheep's wool through a patented process that preserves cysteine in its active form. Keratin hydrolysates, often derived from feathers, are broken down into free amino acids and small peptides. In both cases, the goal is the same: to get sulfur-containing amino acids to the follicle and nail matrix.
Keratin capsules or keratin straightening?
Two things that share only the name. Straightening deposits keratin onto the existing fiber, on the surface, with heat and often fixative agents; the effect is cosmetic, external and temporary, and it does not change the hair that grows afterward. Keratin capsules nourish the follicle that produces the next hair; the effect is internal, progressive and affects the new fiber. One treats the hair's past, the other its future.
The trials
What does the Cynatine HNS trial show?
A randomized, double-blind, placebo-controlled trial in 50 women, 25 per group, for 90 days, two capsules daily of Cynatine HNS at 500 mg with vitamins and minerals, or an identical placebo. The criteria were hair loss, growth, strength, amino acid composition and shine, and nail strength and appearance. The keratin group showed statistically significant improvements compared to placebo for hair and nails. The authors conclude it is an effective supplement within 90 days or less. The trial is registered and one author is affiliated with the manufacturer.
What does the keratin hydrolysate trial show?
A randomized, double-blind, placebo-controlled, multicenter trial in women showing signs of aging, in three groups: 500 mg, 1,000 mg of feather keratin hydrolysate, or placebo, for 90 days. Both doses significantly improved, compared to placebo, roughness, wrinkles, deep hydration, elasticity, thickness and skin density, skin, hair and nail shine, and nail hardness. The authors emphasize that free amino acids act beyond their role as building blocks. Several authors are affiliated with the manufacturer and the testing laboratory.
Does keratin also work on nails?
It is even one of the best-measured effects. Both trials evaluated nails: strength and appearance significantly improved with Cynatine HNS, hardness and shine improved with hydrolysate. The nail is made of the same keratin as hair, and it renews faster, which often makes the effect visible before that on hair.
And on skin?
The keratin hydrolysate trial measured skin in detail: roughness, wrinkles, deep hydration, elasticity, thickness, density and shine, all improved compared to placebo at 90 days. The superficial layer of skin is also made of keratin, and sulfur-containing amino acids participate in its structure. It is a welcome side effect of a supplement taken for hair.
In practice
How long before seeing results?
Both trials lasted 90 days and measured their results at the end. This is consistent with biology: hair grows about one centimeter per month, a fingernail renews in four to six months. The first signs reported, less hair in the brush, nails that break less, often appear within three to six weeks; shine and density require the full three months. Under two months, it is too early to judge.
What dose is needed?
500 mg per day of solubilized keratin is the dose from the Cynatine HNS trial, and the lowest dose from the hydrolysate trial, which also tested 1,000 mg without the higher dose performing clearly better. This is the benchmark for reading a label: a capsule containing significantly less than 500 mg of solubilized keratin does not reproduce what was tested.
How do you know if a keratin is bioavailable?
The label must say something other than keratin. Look for the words solubilized, hydrolyzed, hydrolysate, or a patented ingredient name like Cynatine HNS, which refers to a process and published trials. Keratin simply mentioned, without specifying the form, is most often raw powder, inexpensive and indigestible. Price is a clue: solubilized keratin costs significantly more to produce.
Why combine keratin with zinc and biotin?
Because keratin provides the building blocks, and zinc and biotin are the tools that allow the follicle to assemble them. Zinc is involved in follicle cell division and keratinization enzymes, and it is significantly lower in people experiencing hair loss, 84 versus 98 micrograms per deciliter in 312 patients. Biotin is the cofactor for enzymes that synthesize keratin. Both keratin trials actually combined it with vitamins and minerals.
Vegetarian or vegan, is there a keratin for me?
Keratin is by nature animal: wool, feathers, horns. There is no vegetable keratin, and products that claim it actually provide plant amino acids or plant extracts, which is not the same thing. Solubilized wool keratin is suitable for vegetarians who accept products from shearing, not for vegans. For them, the documented approaches are zinc, biotin, iron and adequate intake of protein and plant-based cysteine.
Limitations and safety
Does keratin regrow hair?
It improves the growth of existing hair and reduces its loss in the Cynatine HNS trial, meaning it acts on active follicles. It does not revive a follicle that has stopped producing, as in established androgenetic baldness. On receding temples or a thinning crown over many years, keratin can improve the quality of remaining hair, not restore lost density: this is a reason for a dermatological consultation.
Are there adverse effects?
Both trials reported no notable adverse effects, and solubilized keratin is a dietary protein, digested into amino acids like any other protein. Precautions relate to other components in a formula: excess zinc can interfere with copper absorption, and certain formulas are inadvisable with anticoagulants. An allergy to wool or feathers is theoretical but worth keeping in mind depending on the keratin source.
What to know about keratin in capsules?
That raw keratin is indigestible and serves no purpose when swallowed, but that solubilized or hydrolyzed keratin is absorbed and has two randomized, double-blind 90-day trials that were positive for hair, nails, and skin. That the studied dose is 500 mg per day and the duration is three months. That form is the only criterion that matters on a label. That it improves growing hair, not established baldness. And that it logically combines with zinc and biotin, the hair follicle cofactors.
Glossary
- Keratin
- Structural protein of hair, nails, and the superficial layer of skin, rich in cysteine; 95% of the hair shaft.
- Cysteine
- Sulfur-containing amino acid whose bonds give keratin its strength; the most valuable building block for the hair follicle.
- Disulfide bond
- A linkage between two sulfur atoms of two cysteines, which locks keratin chains together and makes it indigestible in raw form.
- Solubilized keratin
- Keratin whose disulfide bonds have been opened by a process that preserves peptides and active cysteine; Cynatine HNS is a patented example.
- Keratin hydrolysate
- Keratin broken down by hydrolysis into free amino acids and small peptides, directly absorbable.
- Bioavailability
- The portion of an ingested substance that is actually absorbed and available for tissues.
- Hair follicle
- Structure of the scalp that produces hair; it is what keratin nourishes, not the fiber that has already grown out.
- Nail matrix
- The zone beneath the cuticle where the nail is formed; it renews faster than hair.
- Androgenetic alopecia
- Progressive and localized hair loss, at the temples and crown, through miniaturization and then extinction of follicles; beyond the reach of keratin supplementation.
- Double-blind
- A trial in which neither the participants nor the evaluators know who receives the product or placebo.
Sources
The studies cited below were identified via PubMed.
- Beer C, Wood S, Veghte RH. Clinical trial evaluating the effect of Cynatine HNS on hair and nail parameters. The Scientific World Journal, 2014;2014:641723. One author affiliated with the ingredient manufacturer. DOI
- Tursi F, et al. Effects of oral supplementation with natural keratin hydrolysate on skin aging: a randomized, double-blind, placebo-controlled study in healthy women. Journal of Cosmetic Dermatology, 2025;24(1):e16626. Authors affiliated with the manufacturer and testing laboratory. DOI
- Kil MS, Kim CW, Kim SS. Analysis of serum zinc and copper concentrations in hair loss. Annals of Dermatology, 2013;25(4):405-409. DOI
- Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatology and Therapy, 2019;9(1):51-70. DOI
