Peptide education
Hexapeptide-9
Hexapeptide-9 is a six-residue peptide used in topical skin-care products. Its sequence is Gly-Pro-Gln-Gly-Pro-Gln.
One 10-person experiment compared the peptide with and without a special delivery mixture, with measurements at 10 minutes and one hour. A larger trial tested a different, cyclized form.
Overview
Quick answer
Cyclized hexapeptide-9 has its ends joined into a ring. It is a different chemical form, so its clinical results cannot be assigned to the linear ingredient.
Does the retinol comparison apply to this ingredient?
No. The trial tested a cyclic derivative, not the linear ingredient, against vehicle and a retinol serum at 0.002%.
What was tested in the delivery study?
Ten volunteers had the peptide and a peptide-plus-delivery mixture compared on opposite sides of the face, with measurements at 10 minutes and one hour. The study also included laboratory and animal experiments.
Is skin penetration established for every serum?
No. Penetration depends on the formulation and the skin model used to test it.
Evidence
Evidence snapshot
A delivery mixture was compared with peptide without that mixture, with measurements at 10 minutes and one hour.
The controlled trial used a different molecular form and a low-concentration retinol comparator.
Claims
Common claims vs evidence
| Claim | Human evidence | Mechanistic evidence | Verdict |
|---|---|---|---|
| Hexapeptide-9 has been proven superior to retinol. | A controlled comparison used cyclized hexapeptide-9, not the linear ingredient. | The finding cannot be transferred to this ingredient or all retinol products. | |
| Every product delivers the peptide deeply into skin. | The small clinical comparison tested one delivery mixture. | Laboratory permeation findings came from a specific experimental system. | Skin delivery is formulation dependent. |
Bottom line
Main takeaway
A cyclic form and a linear peptide can share a sequence without being the same molecule.
The delivery mixture and the rest of the formula matter.
Longer vehicle-controlled studies of the linear ingredient are needed for ingredient-level conclusions.
Identity
What it is
The linear peptide has a repeated Gly-Pro-Gln sequence.
Researchers have also examined a ring-shaped derivative with joined termini.
Research
Research evidence
The linear peptide appeared in a small short-term formulation comparison. A separate controlled trial of a cyclic derivative is related evidence, not a direct trial of the same chemical form.
| Study / evidence area | Population | Design | Product context | Main outcome | Limitations | Weight |
|---|---|---|---|---|---|---|
| Peptide delivery experiment | 10 volunteers | Split-face comparison with measurements at 10 minutes and one hour | Hexapeptide-9 with an ionic liquid made from gamma-aminobutyric acid and lactic acid versus peptide without that mixture | The authors reported changes in wrinkle and elasticity measures with the combined preparation at 10 minutes. | Very small sample, short follow-up, and additional active components; no peptide-free vehicle arm was described. | Limited formulation-level human evidence |
| Cyclized derivative trial | 96 randomized adults, 91 completers | Randomized, double-blind, three-arm comparison over 56 days | Cyclic hexapeptide-9 serum, retinol serum, or vehicle | The cyclic serum improved several wrinkle measurements in the reported comparison. | The cyclic derivative is a different form; the retinol comparator was 0.002% and follow-up was short. | Related derivative evidence, not direct evidence for linear hexapeptide-9 |
Cautions
Safety and unknowns
- The delivery study reported no allergic reactions in patch testing of its preparations. Small, short tests cannot exclude uncommon or delayed effects.
- Safety findings for the cyclic derivative cannot automatically be applied to the linear ingredient.
Product quality
Product identity and quality
Ingredient form and delivery system affect which studies are relevant to a product.
Linear or cyclic
Joining the peptide ends creates a different chemical form.
Delivery system
Experimental penetration results depend on the tested mixture.
Mechanism
How it is proposed to work
Researchers study this peptide in skin-delivery and collagen-related models. Results in a laboratory do not establish a clinical effect for every serum.
A delivery mixture altered penetration in an experimental skin system.
The cyclic derivative was designed to alter properties of the linear peptide.
Details
Technical details
Sources
References
- 1.
PubMed Central. Pioneering ionic liquids in neuro-soothing: Enhanced transdermal delivery of collagen peptides and their synergistic anti-aging functions
doi:10.1016/j.mtbio.2025.101527 PMID:39968525
Laboratory, animal, and 10-person split-face experiments; human measurements included 10 minutes and one hour after application.
- 2.
PubMed Central. Novel Cyclized Hexapeptide-9 Outperforms Retinol Against Skin Aging: A Randomized, Double-Blinded, Active- and Vehicle-Controlled Clinical Trial
doi:10.1111/jocd.70290 PMID:40586182
A trial of cyclized hexapeptide-9, a chemically modified form, not linear hexapeptide-9.
- 3.
FDA. Is It a Cosmetic, a Drug, or Both? (Or Is It Soap?)
US product classification depends on intended use.