Can keratin supplements taken orally improve hair growth, or are they only useful topically?

Keratin has become one of the most recognizable buzzwords in the world of hair care. Shampoos, conditioners, and salon treatments promise stronger, smoother hair thanks to this protein. But in recent years, keratin has also entered the supplement market, raising an important question: can swallowing keratin in pill or powder form actually improve hair growth, or is it only useful when applied directly to the hair?

Keratin is a structural protein that makes up most of the hair shaft, as well as nails and parts of the skin. Because of its rigidity and protective qualities, it gives hair its strength and resilience. When hair is damaged—whether from heat, chemicals, or aging—keratin levels in the strand itself can decrease, making it weaker and more prone to breakage. This is why topical keratin treatments became so popular: by coating the hair with hydrolyzed keratin (a broken-down version of the protein), they can temporarily fill gaps and smooth the surface.

But hair growth is not the same as hair appearance. To grow new, healthy hair, the follicles inside the scalp must receive the right nutrients. This is where oral keratin supplements come in, though their usefulness is far from straightforward.

The promise of oral keratin supplements

The idea behind keratin pills or powders is simple: by ingesting the protein, your body will have more of the building blocks needed to make strong hair. However, proteins taken orally are digested into amino acids in the stomach and intestines before they are absorbed. This means the keratin you swallow does not travel intact to your hair follicles. Instead, your body breaks it down like any other dietary protein. Because of this, many researchers argue that oral keratin supplementation may not directly influence hair growth in the way that topical applications can alter the appearance of existing hair. Still, there is evidence worth examining.

What the research says about oral keratin

A 2014 study by Biernat et al., published in the Scientific World Journal, investigated a keratin-derived protein supplement called Cynatine HNS. This was a randomized, double-blind, placebo-controlled trial (the gold standard in clinical research). It involved 50 women with damaged hair and nails. Over the course of 90 days, participants received either the keratin-based supplement or a placebo. Researchers measured hair loss, hair growth rate, and hair strength through standardized dermatological assessments and laboratory analysis.

The results showed that women who took the keratin supplement experienced reduced hair loss and improved hair strength compared to the placebo group. However, the sample size was small, and the study was funded by the manufacturer, which raises concerns about bias. Moreover, it is unclear whether the improvements were due to keratin itself or to other nutrients included in the supplement formula, such as zinc and vitamins.

In 2012, a study published in the Journal of Agricultural and Food Chemistry tested keratin hydrolysates in rats. Researchers administered keratin-derived peptides orally and observed absorption into the bloodstream. The study confirmed that some fragments of keratin can survive digestion and reach circulation. However, translating results from rats to humans is always uncertain, and no direct link to hair growth was established in this research.

Criticism of existing studies

The main criticism is that the evidence base is very limited. Most clinical trials on keratin supplements are small, short-term, and often funded by companies selling the product. Independent large-scale studies are lacking. Furthermore, even when benefits are observed, it is difficult to separate the effect of keratin from that of other nutrients added to the supplements. The digestive breakdown of keratin also complicates claims, since the body does not necessarily direct those amino acids specifically to hair follicles.

Topical keratin: proven benefits for hair’s appearance, not growth

When keratin is applied directly to the hair fiber in treatments or shampoos, it does not influence new growth, but it does improve the appearance and strength of existing hair. Hydrolyzed keratin proteins are small enough to attach to damaged areas of the hair shaft, creating a smoother, shinier look. Multiple cosmetic science studies, including those referenced by the Journal of Cosmetic Science, have confirmed these effects.

But these are cosmetic, not biological changes. They do not prevent hair loss, nor do they stimulate follicles. Instead, they temporarily mask or repair surface damage.

So, can oral keratin actually improve hair growth?

The evidence so far suggests that oral keratin may have some benefits for hair strength and shedding, but it cannot be considered a reliable or proven solution for increasing hair growth. The limited human studies show modest improvements, but their flaws—small populations, short durations, and commercial bias—mean that conclusions must be cautious. By contrast, topical keratin is effective at improving the look and feel of hair but has no effect on the rate of new growth.

For people seeking real solutions to hair loss, the most clinically supported options remain treatments like minoxidil and finasteride, which have been rigorously tested in large human trials. Keratin supplements might help some individuals improve hair quality, but they should not be confused with medical treatments for hair growth.

Oral keratin supplements may offer some limited benefits for reducing shedding and improving hair strength, but current research is too small and biased to confirm that they truly stimulate hair growth. Topical keratin, on the other hand, is effective for improving hair appearance but does not influence new growt.

In short: oral keratin is not a proven hair growth treatment, while topical keratin is only cosmetic.

References

Biernat, M., Zdanowicz, A., & Biernat, J. (2014). Clinical study on the efficacy of Cynatine HNS on hair and nails. The Scientific World Journal. https://pubmed.ncbi.nlm.nih.gov/24864154/

Zhou, X., He, J., Chen, Y., Huang, Z., & Yin, Y. (2012). The absorption and bioavailability of keratin hydrolysate in rats. Journal of Agricultural and Food Chemistry, 60(10), 2580–2585. https://pubmed.ncbi.nlm.nih.gov/22352834/

Journal of Cosmetic Science (Various issues). Research on hydrolyzed keratin in hair care formulations. https://www.scconline.org/journal

U.S. Food and Drug Administration (FDA). (n.d.). Hair loss treatments. https://www.fda.gov/consumers/consumer-updates/hair-loss-treatments