Multi-Peptide Serum for Hair Density: Does It Work?

The Ordinary's Multi-Peptide Serum for Hair Density lists eight named actives — REDENSYL, Procapil, CAPIXYL, BAICAPIL, AnaGain, caffeine and two peptides. Kérastase's Genesis serum lists four. Tara's Follicle-Stimulating Scalp Serum is a peptide serum too — the same class of actives. The difference is the question almost nobody answers: how much of the active is actually in the bottle?

Does a multi-peptide serum actually work?

The honest answer: one combination has earned a real trial. In an independent, 24-week, triple-blind randomised trial, a biochanin-A + acetyl-tetrapeptide-3 combination — the same molecules as CAPIXYL™ — raised terminal hair count 8.3%, statistically level with 3% minoxidil (8.7%), in 32 subjects with pattern hair loss [1]. The mechanism has independent support too: biochanin A inhibits the type-2 5α-reductase enzyme that dominates the scalp follicle, in university laboratory work with no supplier involvement [2].

That is the strongest evidence in this product class. Most of the rest — including the famous percentages on supplier brochures — is manufacturer-funded and was generated at specific doses.

The dose decides — a label is not a dose

Here is the factor almost every comparison skips: a peptide on the INCI list tells you it's present, not that there's enough of it for the trial data to apply. CAPIXYL's clinical data was generated at its working level — the supplier's specified range is 3–5% of the finished formula. Below 3%, citing that study is overreach.

The same gate cuts in both directions, including against us. The "121% faster growth" figure that circulates for biotinoyl tripeptide-1 comes from the single peptide at 5 ppm in ex-vivo organ culture — not a finished serum, not at a finished-product dose, not on a human head. We don't use that number. The famous "87% regrowth" onion figure comes from crude onion juice on alopecia areata, an autoimmune condition — it does not transfer to any cosmetic-dose extract, so we don't use that one either. And hydrolyzed keratin's fibre-repair data is ex-vivo and washes out over subsequent shampoo cycles — so it earns a supporting role, not a headline.

Tara's claims are dose-gated. Every claim on this page passed a dose check before it shipped: if the active weren't at its studied working level, the claim would not exist — not on this page, not on the bottle. Our serum runs CAPIXYL at 5% — inside the 3–5% range the clinical data was built on.

Tara's isn't bare peptides — here's the rest of the bottle

• Acetyl Tetrapeptide-3 + biochanin A (CAPIXYL™) at 5% — the dose-correct version of the only peptide combination with an independent head-to-head against minoxidil [1].
• Red onion extract — the collection's identity botanical: an organosulphur, quercetin-rich scalp-environment active, honestly framed (see what it does NOT do, below).
• Inositol at 0.9% — a B-family scalp-conditioning factor at a deliberate, named dose.
• Hydrolyzed keratin — low-molecular-weight fibre support; ex-vivo evidence, re-applied with each use because the effect washes out [3].
• A B-vitamin multivitamin complex — antioxidant support during wear.

The Ordinary vs. Kérastase vs. Tara

Competitor rows reflect each brand's own product page as fetched on 11 June 2026; if they publish doses tomorrow, this table should change.

How to use it

Apply one dropper directly to the scalp on dry or towel-dried hair, massage in with fingertips, and leave in — once daily. Pair it with a gentle wash routine; the serum is the step that stays on the scalp and works between washes. Find it in the Onion + Peptides collection or go straight to the Follicle-Stimulating Scalp Serum.

What it does NOT do

This serum is not a treatment for alopecia areata, androgenetic alopecia, or any diagnosed condition. The onion here is a scalp botanical — the famous "87% regrowth" onion figure comes from crude onion juice on alopecia areata and does not transfer to a cosmetic-dose extract. The keratin supports the fibre and washes out; it does not rebuild hair from within. And no leave-in serum, ours included, reverses an established medical hair-loss condition. What the data supports: a dose-correct peptide combination that held its own against 3% minoxidil over 24 weeks in an independent trial. That is the claim, and that is the whole claim.

So which should you buy?

Want bare peptides at the lowest price? Buy the cheapest one — the complexes are the same names. Want a salon brand with a regimen behind its number? Kérastase's figure belongs to its three-product routine. Want the one peptide combination with an independent trial, at the dose the trial used, with the funding disclosed and the un-claims printed next to the claims? That is the serum we make.

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[1] Lueangarun S, Panchaprateep R. J Clin Aesthet Dermatol 2020;13(10):32–37. PMID 33584955. · [2] Hiipakka RA et al. Biochem Pharmacol 2002;63(6):1165–1176. PMID 11931850. · [3] Single-fibre tensile data on hydrolyzed keratin, ex-vivo; effect washes out across shampoo cycles (industry consensus, Robbins 2012). · [4] Sharquie KE, Al-Obaidi HK. J Dermatol 2002;29(6):343–346. PMID 12126069 (the onion/alopecia-areata receipt — cited here as the figure we do NOT use).