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Limited evidenceJoints & skin

Keratin

Oral keratin (usually solubilized wool keratin, sold as Cynatine HNS) rests on a single small manufacturer-funded trial; the intuitive idea that eating hair protein makes hair is not how protein digestion works.

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What the science says

  • Reduces hair loss and improves hair strength Limited evidence

    The one placebo-controlled trial commonly cited enrolled 50 women on 500 mg/day of solubilized keratin for 90 days and reported improvements in hair loss, hair strength, luster and nail appearance. It is small, short, industry-sponsored and has not been independently replicated — the definition of a limited evidence base.

  • Improves nail hardness and growth Limited evidence

    Nail outcomes in that same 50-person trial were secondary and largely subjective or investigator-rated. A 2023 systematic review of nutritional supplements for hair complaints found the field dominated by small, low-quality, sponsor-funded studies, and keratin was not among the ingredients with reproducible support.

  • Eating keratin delivers keratin to your hair Limited evidence

    Ingested keratin is digested to amino acids and small peptides like any other protein; it is not routed preferentially to follicles. Keratin is cysteine-rich, so a plausible framing is that it supplies sulfur amino acids — but adequate dietary protein already does this, and cysteine supplementation alone has not been shown to improve hair in well-nourished people.

Dosage & safety

Studied dose500 mg/day of solubilized keratin for 90 days is the dose used in the published trial. Products commonly supply 250-500 mg, usually bundled with biotin, zinc, copper and vitamin C, which makes attributing any effect to keratin itself impossible. Give any hair supplement at least 3-6 months before judging it — the hair cycle is that slow.
SafetyNo serious adverse effects reported at 500 mg/day; mild GI upset is the usual complaint. Sourced from sheep's wool, so it is not vegetarian and is a theoretical concern for wool/lanolin-sensitive individuals. The bigger practical risk is the high-dose biotin (often 5,000-10,000 mcg) packaged alongside it, which interferes with immunoassays and has caused falsely low troponin results and missed myocardial infarctions — stop biotin-containing products several days before blood testing. Sudden or patchy hair loss warrants a medical workup (iron deficiency, thyroid disease, androgenetic alopecia) rather than a supplement.

How to take it

TimingTiming does not matter.
With food?With food, which limits the mild GI upset some people get.
Worth knowingJudge it at 3-6 months, not weeks — and stop the high-dose biotin it is bundled with several days before any blood test.

Frequently asked questions

Do keratin supplements reduce hair loss?

Oral keratin rests on a single small, manufacturer-funded trial (limited evidence): 50 women taking 500 mg/day of solubilized keratin for 90 days reported less hair loss and stronger hair. The result has not been independently replicated.

Does eating keratin make your hair stronger?

Ingested keratin is digested into amino acids and small peptides like any other protein and is not routed preferentially to hair follicles. Keratin is rich in cysteine, but adequate dietary protein already supplies sulfur amino acids, and cysteine alone has not been shown to improve hair in well-nourished people.

How long does keratin take to work for hair?

The published keratin trial used 500 mg/day for 90 days, and any hair supplement needs at least 3-6 months before you judge it because the hair cycle is slow. Keratin products are usually bundled with biotin, zinc and other nutrients, making any effect impossible to attribute to keratin itself.

Are keratin supplements safe?

No serious adverse effects of keratin have been reported at 500 mg/day, and mild GI upset is the usual complaint. The bigger risk is the high-dose biotin often packaged with it, which distorts lab tests such as troponin, so stop biotin-containing products several days before blood tests.

Scientific references

Where to buy

Double Wood Supplements, Keratin, 120 Capsules (250 mg per Capsule)

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