Part of the skin and hair peptide hub: every topical and cosmetic peptide we cover, with its evidence grade.
Tetrapeptide-30
Pro-Lys-Glu-Lys, a skin-lightening cosmetic peptide whose human studies were run by scientists from the company that makes it
Tetrapeptide-30 is the cosmetic ingredient name for PKEK, four amino acids that in skin cells lowered the inflammatory and pigment-signalling genes switched on by ultraviolet light. Double-blind studies on volunteers found it faded pigment spots, mainly when combined with the whitening agent sodium ascorbyl phosphate, and evened facial skin tone in people with dark skin and melasma. Every human study so far was written by scientists from the ingredient's supplier, and none states the concentration used. Later laboratory work shows the peptide crosses the skin barrier poorly from an ordinary cream.
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Recommended Dosing
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What is it?
Skin darkens after sun exposure partly because damaged keratinocytes, the main cells of the outer skin, release signals that tell pigment cells to make more melanin. One of those signals, alpha-MSH, is cut from a larger precursor protein called POMC. PKEK was put forward as a way to quieten that conversation: in human keratinocytes exposed to UVB light, adding the peptide significantly reduced the messenger RNA for the inflammatory signals IL-6, IL-8 and TNF-alpha and, the authors stress, for POMC itself.
The main paper, published in 2012, then reports four double-blind, vehicle-controlled studies in people. In 10 healthy volunteers who applied PKEK once a day for four weeks, a later UVB exposure switched on fewer inflammatory and pigment genes in the skin, including the genes for POMC and tyrosinase, the enzyme that makes melanin. The other three tested pigment spots. In 39 women, facial spots faded significantly after six weeks when PKEK was combined with sodium ascorbyl phosphate, a vitamin C derivative used as a whitener, and less with either ingredient alone. On the backs of the hands of 19 people, adding PKEK made a sodium ascorbyl phosphate preparation work better over eight weeks, and in 27 Japanese women, treated with either the whitener alone or the combination, the combined cream significantly reduced pigmentation over eight weeks. So most of the clinical evidence is for the pair, not for PKEK by itself.
A separate 2011 study tested PKEK on its own against its vehicle in South Africa, in people with skin types V and VI who had melasma or darkening left after inflammation. Expert graders comparing standardised photographs found the peptide formulation significantly better than the vehicle at 12 weeks for overall appearance and evenness of tone. The abstract gives no participant numbers, no concentration and no size of the effect. Its first author, and two authors of the 2012 paper, are scientists at the company that supplies the ingredient, so these are supplier-sponsored studies that no independent group has repeated.
Since then the literature has been about delivery. On excised human skin, most of the PKEK that entered from a standard cream stayed in the outermost dead layer, while a water-in-oil microemulsion carried far more into and through the skin; later work used PKEK as a model peptide to compare skin membranes and penetration enhancers, and a 2022 review lists it among cosmetic peptides whose effects in cells are of little use unless they reach living skin. For a buyer, tetrapeptide-30 is a cream ingredient with a plausible mechanism and supplier-run evidence that it helps a vitamin C whitener; how much reaches the pigment cells depends on the product's formulation, which a label does not reveal.
At a Glance
Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.
Published Research
These are the studies of tetrapeptide-30 read from their PubMed abstracts on October 29, 2026: two papers reporting human studies, both authored with the supplier's scientists, three laboratory studies of skin penetration and one review. The review is carded because its abstract names PKEK among the peptides it assessed.
Cells plus four controlled volunteer studies
In UVB-exposed keratinocytes PKEK lowered IL-6, IL-8, TNF-alpha and POMC messenger RNA. In 10 volunteers pretreated once daily for four weeks it blunted UVB-induced IL-1alpha, IL-6, IL-8, TNF-alpha, POMC and tyrosinase genes. With sodium ascorbyl phosphate it faded facial spots in 39 women at six weeks more than either alone, boosted the whitener on the hands of 19 people over eight weeks, and in 27 Japanese women reduced pigmentation by 26% (18% by SCINEXA score). Two authors also wrote the supplier's 2011 study.
Darker skin with melasma: peptide versus vehicle
In a double-blind, vehicle-controlled study in South Africa of people with skin types V-VI and facial melasma or post-inflammatory hyperpigmentation, experts grading digital images rated the PKEK formulation significantly better than vehicle at 12 weeks for overall appearance (P < 0.05) and evenness of tone (P < 0.01). The first author's affiliation is the ingredient's supplier.
Cream versus microemulsion on human skin
On excised human skin, 40-58% of the PKEK in a standard cream entered the skin, but most stayed in the stratum corneum and did not reach the living layers. From a water-in-oil microemulsion, 94% had penetrated by 100 minutes and 88% by 300 minutes, mostly passing right through; the amounts left in the living layers were similar for both. Two authors are from the supplier.
Choosing a test membrane
Using a 10% PKEK solution as the model substance, the authors measured its passage through isolated human stratum corneum, sunburned stratum corneum, pig stratum corneum and shed snake skin by infrared spectroscopy, and concluded that snake skin can stand in for human skin in this kind of permeation test.
Penetration enhancers on snake skin
Through shed snake skin, PKEK passed faster in the presence of 10% dimethyl sulfoxide than on its own; propanediol, butanediol and the longer-chain diols made no significant difference to its permeation.
Skin permeability of anti-wrinkle peptides
A review of why cosmetic peptides, PKEK among them, penetrate skin poorly and of the chemical, physical and carrier methods tried to improve it; it concludes that effects seen in cells mean little unless enough peptide reaches its target, which most cannot do without help.
Side Effects & Contraindications
Reported Side Effects
From the abstracts read, which say little about safety.
Contraindications & Cautions
A cosmetic ingredient, not a medicine, so there is no label.
Legal Status
A cosmetic ingredient, not a drug.
Frequently Asked Questions
?What is tetrapeptide-30?
The cosmetic ingredient name for PKEK (proline, lysine, glutamic acid, lysine), a four-amino-acid peptide used in skin-lightening products.
?Does it lighten skin?
In supplier-authored double-blind studies it reduced pigment spots, mostly when combined with the whitener sodium ascorbyl phosphate, and evened facial tone in people with dark skin and melasma compared with a vehicle cream. No independent study has repeated these results.
?What concentration is used?
None of the human study abstracts states one. A laboratory test of skin permeation used a 10% solution of the peptide as a model substance; that was chosen to measure penetration, not to treat skin.
?Does it get into the skin?
Poorly from an ordinary cream: on excised human skin most of it stayed in the outermost dead layer. A microemulsion carried much more into and through the skin, so the formulation matters as much as the peptide.
References
- [other] PubChem CID 25001762, Tetrapeptide-30: formula C22H40N6O7, molecular weight 500.6. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/25001762
- [clinical-trial] Marini A, et al. "Modulation of skin pigmentation by the tetrapeptide PKEK: in vitro and in vivo evidence for skin whitening effects." Exp Dermatol, 2012;21(2):140-6. PMID: 22142309.
- [clinical-trial] Farwick M, et al. "Facial skin-lightening benefits of the tetrapeptide Pro-Lys-Glu-Lys on subjects with skin types V-VI living in South Africa." J Cosmet Dermatol, 2011;10(3):217-23. PMID: 21896134.
- [pubmed] Neubert RHH, et al. "Dermal peptide delivery using enhancer moleculs and colloidal carrier systems. Part II: Tetrapeptide PKEK." Eur J Pharm Biopharm, 2018;124:28-33. PMID: 29247690.
- [pubmed] Foerster AC, et al. "Dermal Peptide Delivery Using Enhancer Molecules and Colloidal Carrier Systems - Part IV: Search for an Alternative Model Membrane for Future ATR Permeation Studies Using PKEK as the Model Substance." Skin Pharmacol Physiol, 2019;32(3):151-161. PMID: 30943494.
- [pubmed] Foerster A, et al. "Dermal peptide delivery using enhancer molecules and colloidal carrier systems - part V(#): Influence of enhancers on the permeation of PKEK through snake skin." Pharmazie, 2019;74(3):136-141. PMID: 30961677.
- [review] Mortazavi SM, et al. "Skin permeability, a dismissed necessity for anti-wrinkle peptide performance." Int J Cosmet Sci, 2022;44(2):232-248. PMID: 35302659.
Sources & Citations
Every study on this page was read from its PubMed record on October 29, 2026. Studies whose authors work for the ingredient's supplier are labelled as such. Concentrations are printed only where a study used them; no supplier's figure is used. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Consult a licensed healthcare provider before making health decisions.