tetrapeptide-21
GEKG, Gly-Glu-Lys-Gly, glycyl-glutamyl-lysyl-glycine
Tetrapeptide-21 is a four-residue synthetic peptide, glycine-glutamate-lysine-glycine, designed in silico from extracellular matrix protein sequences and marketed as a collagen and hyaluronan stimulator. It is one of the few cosmetic peptides in this group with a published, placebo-controlled human study, though that study is small, was authored by the ingredient's developers, and was published as a short letter rather than a full trial report.
Mechanism
GEKG was selected by molecular design as a short motif abstracted from extracellular matrix protein sequences rather than as a fragment of a specific parent protein with known receptor pharmacology. Farwick and colleagues reported that in human dermal fibroblasts it increased collagen production at both messenger RNA and protein level; the broader rationale advanced for it includes upregulation of fibronectin and hyaluronan synthase, with increased hyaluronan contributing to dermal hydration and volume. No specific receptor has been identified, and the signalling route between peptide and transcriptional change has not been mapped. That is a real gap: without a receptor it is difficult to distinguish a genuine signalling effect from a nutritional or physicochemical one, and difficult to predict dose-response behaviour.
Delivery has attracted more attention than mechanism. GEKG is small, extremely hydrophilic and carries both a negative charge from glutamate and a positive charge from lysine, making passive diffusion through the stratum corneum unfavourable. Sommer and colleagues devoted a paper specifically to dermal delivery of GEKG using chemical penetration enhancers and colloidal carrier systems, and Stephenson and colleagues subsequently developed elastin-derived peptide hydrogels for sustained dermal delivery. The existence of this delivery literature is itself informative: unassisted penetration is the limiting problem, and a plain aqueous serum is unlikely to solve it.
What the research shows
Farwick and colleagues reported in Experimental Dermatology that GEKG, developed from an in silico molecular design approach, significantly enhanced collagen production at both messenger RNA and protein level in human dermal fibroblasts. The human component comprised a double-blind, randomised, placebo-controlled study in 10 volunteers with an average age of 48.2 years, plus a separate investigation in 30 volunteers using three-dimensional fringe projection to quantify facial wrinkling, in which GEKG but not placebo significantly decreased skin roughness. Read carefully, this is a positive result in a very small sample using a surface-roughness surrogate endpoint, published as a short communication.
The subsequent literature is about getting the peptide into skin rather than about confirming that it works. Sommer and colleagues characterised dermal delivery of GEKG using enhancer molecules and colloidal carriers as the third part of a series on peptide delivery, quantifying how poorly the free peptide penetrates and how much specific systems improve it. Stephenson and colleagues developed elastin-derived peptide hydrogels for sustained dermal release. A 2025 in vitro study by Paccola and colleagues examined bioactive peptides combined with injectable platelet-rich fibrin on fibroblast viability and extracellular matrix gene expression. The peptide also appears as a scaffold in Park and colleagues' D-tyrosine work. What has not appeared is an independent clinical replication.
Evidence assessment
Limited evidence
There is one published human study with a randomised, double-blind, placebo-controlled component, which puts this ahead of most peptides in this group. But it enrolled only 10 volunteers in the controlled arm, with a separate 30-participant assessment using three-dimensional fringe projection; it was authored by researchers at the company that developed the ingredient together with academic collaborators, and PubMed indexes it as a Letter rather than a full trial report. No independent group has replicated the clinical finding in the fifteen years since. A single small developer-authored controlled study is the textbook case for 'limited'.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Bioactive tetrapeptide GEKG boosts extracellular matrix formation: in vitro and in vivo molecular and clinical proof Preclinical only
GEKG significantly induced collagen production at mRNA and protein level in fibroblasts, and GEKG but not placebo significantly decreased skin roughness as a measure of wrinkles.
Dermal peptide delivery using enhancer molecules and colloidal carrier systems. Part III: Tetrapeptide GEKG Preclinical only
Characterised the poor intrinsic dermal penetration of free GEKG and quantified the improvement achievable with chemical enhancers and colloidal carriers.
Elastin-derived peptide hydrogels for sustained dermal delivery of tetrapeptide-21 Preclinical only
Developed elastin-derived peptide hydrogels providing sustained dermal delivery of tetrapeptide-21.
Synergistic Effects of Injectable Platelet-Rich Fibrin and Bioactive Peptides on Dermal Fibroblast Viability and Extracellular Matrix Gene Expression: An In Vitro Study Preclinical only
Assessed combinations of bioactive cosmetic peptides with injectable platelet-rich fibrin on fibroblast viability and extracellular matrix gene expression.
Safety
No safety concerns have been reported. The peptide is composed entirely of common proteinogenic amino acids with no unusual residues, no lipid modification and no reactive chemistry, and glycine, glutamate and lysine are dietary amino acids. No sensitisation, phototoxicity, reproductive or developmental data have been published, and there are no human pregnancy or lactation data. Where the peptide is formulated with chemical penetration enhancers or colloidal carriers to overcome its poor permeability, the safety assessment of the finished product should address the enhancer system as well as the peptide, since penetration enhancers alter barrier function and can themselves cause irritation. This is a topical cosmetic ingredient and has not been evaluated for injection.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Permitted as a cosmetic ingredient under the UK Cosmetics Regulation (retained Regulation (EC) No 1223/2009); not listed in any prohibited or restricted annex. Requires a Cosmetic Product Safety Report and responsible person, and that assessment should cover any penetration enhancer system used alongside it. No MHRA medicines authorisation. |
| United States | Not an FDA-approved drug and not covered by an OTC drug monograph; marketed as a cosmetic ingredient under the FD&C Act as amended by the Modernization of Cosmetics Regulation Act 2022. Cosmetic ingredients are not pre-approved, but structure-or-function claims can render a product an unapproved drug. |
| WADA (sport) | Not named on the WADA Prohibited List. Topical cosmetic use raises no anti-doping issue. |
Questions
Yes, though a small one. The 2011 Experimental Dermatology report included a double-blind, randomised, placebo-controlled arm with 10 volunteers plus a 30-participant roughness assessment, and found a significant reduction in skin roughness versus placebo. It was published as a short letter by the ingredient's developers with academic collaborators and has not been independently replicated in fifteen years.
Not well on its own. It is a small, doubly charged, highly water-loving peptide, and a dedicated permeation study found it needs chemical enhancers or colloidal carriers to reach the dermis in meaningful amounts. Subsequent research has focused on hydrogel delivery systems for the same reason.
None has been identified. The peptide was designed in silico from extracellular matrix sequences rather than derived from a protein with known receptor pharmacology, and the signalling route between the peptide and the reported increases in collagen and hyaluronan synthase has not been mapped.
No safety concerns have been reported. It is built from three ordinary dietary amino acids with no unusual chemistry. Where it is formulated with penetration enhancers to compensate for its poor permeability, the enhancer system deserves as much safety scrutiny as the peptide.