Collagen and peptides for hair growth: what the evidence shows

What did @twiceasgoodhair actually say?

The creator made two connected arguments: first, that marine collagen (from fish scales) is specifically better for hair, skin, and nails than bovine collagen (from cows), which they say is "more geared towards joints." Second, they called collagen "the best supplement" for hair growth, full stop, recommending marine collagen peptides as their single top pick.

To their credit, they correctly identified the sourcing difference. Marine collagen is predominantly Type I collagen, derived from fish skin and scales. Bovine collagen contains both Type I and Type III. The creator is at least working from a real biological distinction, not inventing one. But the leap from "different source" to "better for hair" is where things get shaky.

Does the science back this up?

Partially, and with serious caveats. The evidence for collagen supplementation improving hair outcomes is thin and often industry-funded. There is no large, independent randomized controlled trial confirming marine collagen specifically outperforms bovine collagen for hair growth in head-to-head comparison.

A 2019 study by Hexsel et al. published in the Journal of Cosmetic Dermatology found that specific collagen peptides improved nail growth and reduced breakage, which is adjacent but not identical to hair growth. A 2020 review by Bolke et al. in Nutrients looked at a marine collagen supplement and found improvements in skin elasticity, but hair outcomes were secondary endpoints with modest effect sizes. The mechanism proposed is that hydrolyzed collagen peptides may stimulate fibroblasts and provide amino acid precursors, particularly glycine and proline, for keratin synthesis. That is biologically plausible. It is not the same as proven.

• Most studies use proprietary hydrolyzed collagen blends, making source comparisons difficult.
• Hair growth studies often rely on self-reported outcomes or small sample sizes.
• Few studies isolate marine collagen against bovine in a direct hair-focused trial.

What did they get wrong (or right)?

They got the sourcing taxonomy right. Marine collagen is predominantly Type I, which is the dominant collagen type in skin and hair follicle structures. Bovine collagen does contain more Type III, which is associated with connective tissue and joints. That part holds up.

What is misleading is framing bovine collagen as "more geared towards joints" as if it cannot benefit hair or skin. Bovine Type I collagen is still Type I collagen. The amino acid profiles between marine and bovine hydrolysates are similar enough that the clinical difference for hair specifically has not been established in well-controlled trials. Saying marine is definitively better for hair is a reasonable hypothesis, not a proven conclusion.

Calling collagen "the best supplement for hair growth" is a strong claim that the evidence does not fully support. Treatments with far more robust evidence for hair loss, like minoxidil or finasteride, are prescription-adjacent or regulated. Among over-the-counter supplements, biotin, iron (in deficient individuals), and vitamin D all have comparable or stronger evidence bases depending on the cause of hair loss. Collagen is not nothing, but "best supplement" is a stretch.

What should you actually know?

The type of collagen you take matters less than addressing why your hair is struggling in the first place. Hair loss has many causes, including androgenetic alopecia, telogen effluvium, thyroid dysfunction, iron deficiency, and autoimmune conditions. No supplement, marine or otherwise, addresses those root causes.

If you are choosing between marine and bovine collagen, marine is a reasonable choice if you prefer a Type I-dominant product. The bioavailability of hydrolyzed marine collagen peptides is well-documented, and some researchers argue the smaller peptide size improves absorption (Yamada et al., 2021, Marine Drugs). But "better absorbed" is not the same as "proven to grow hair faster."

Collagen supplements are generally safe for most people. They are not regulated as drugs. If you have a fish allergy, marine collagen is an obvious contraindication. And if your hair loss has a medical cause, a supplement is not a substitute for a proper diagnosis.

• Get bloodwork done before spending money on any hair supplement.
• Collagen provides amino acid building blocks but does not directly stimulate hair follicles the way clinically validated treatments do.
• The "marine is better for hair" claim is plausible but not proven in head-to-head clinical trials.