What is Tetrapeptide-21?
Tetrapeptide-21 is the four-amino-acid peptide GEKG: glycine, glutamic acid, lysine and glycine. It is sold for anti-ageing and collagen support.
It has been studied alongside platelet-rich fibrin, a blood-derived concentrate investigated for facial rejuvenation.
How it is thought to work
In a 2025 cell study, GEKG combined with platelet-rich fibrin increased fibroblast viability and changed the activity of genes linked to the extracellular matrix. The authors say this was the strongest combination tested.
A 2020 study added a D-tyrosine to the end of GEKG. The modified peptide reduced melanin in cells, and the authors report that this did not change the peptide’s other effects. The modified form is a different molecule from plain tetrapeptide-21.
What the studies show
Every record below was checked against the paper. Where a result is from cells, animals or a combination product, the entry says so.
Paccola AGL, et al. Molecules. 2025;30(16). (opens in a new tab)
Design. In vitro study on human dermal fibroblasts over 72 hours, with tetrapeptide-21 alone and with platelet-rich fibrin.
Finding. The combination with platelet-rich fibrin gave the strongest effects on cell viability and extracellular matrix gene activity.
Park J, et al. Sci Rep. 2020;10(1):262. (opens in a new tab)
Design. Human melanoma cells, primary melanocytes and a 3D human skin model, testing D-tyrosine-modified peptides.
Finding. Adding D-tyrosine to GEKG gave an anti-melanin effect in cells without changing its intrinsic anti-ageing effect. The modified peptide is not plain tetrapeptide-21.
How it is used
Found in some anti-ageing serums and eye products, sometimes with other peptides. Look for GEKG or Tetrapeptide-21 on the label.
Concentrations used in products are not in the records checked for this page.
Safety
No human safety data for this peptide alone appear in the records checked. The cell studies report cell viability, not skin reactions.
Patch-test before regular use, especially on sensitive skin.
Talk to a doctor, dermatologist or pharmacist before starting a new active, especially if you are pregnant, have a skin condition, or use prescription treatments.
Questions
What is GEKG?
GEKG is the one-letter code for the four amino acids glycine, glutamic acid, lysine and glycine. Tetrapeptide-21 is the INCI name for the same peptide.
Is it proven to reduce wrinkles?
No. The records checked for this page include cell studies of collagen-related activity and a melanin study, but no controlled human wrinkle trial of the peptide alone.