Rigin

Dosing from the Literature

Published for skin: cosmetic use concentrations, put at under 10 ppm of peptide by a safety review, often inside Matrixyl 3000. Not published: a trial of Rigin alone.

Rigin is a topical cosmetic ingredient, so it has no dose in the drug sense, only a concentration in a finished product. Rigin, Sederma's trade-name mixture, contains 500 ppm (0.05%) palmitoyl tetrapeptide-7, and the industry's survey of use concentrations did not include the peptide; the Cosmetic Ingredient Review's panel took peptide use of 1–30 ppm, under 10 ppm being customary, as typical for it (Johnson et al., 2018).

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What It Is

Rigin is the trade name, owned by Sederma (a subsidiary of Croda International), for the cosmetic active ingredient palmitoyl tetrapeptide-7 — a synthetic lipopeptide consisting of a four-residue peptide sequence (glycyl-glutaminyl-prolyl-arginine, Gly-Gln-Pro-Arg, GQPR) covalently coupled at the N-terminus to a sixteen-carbon saturated palmitic acid chain. The parent GQPR sequence is a natural fragment of immunoglobulin G (IgG) antibodies (Johnson et al., 2018) and belongs to a family of small immunomodulatory (adjusting the immune system up or down) peptides cut from IgG (the "tuftsin family"), studied since tuftsin was described in 1970 (Najjar & Nishioka, 1970). The palmitoyl moiety increases the molecule's lipophilicity and is the standard Sederma approach to improving stratum corneum penetration of an otherwise polar peptide.

The compound is assigned INCI name "Palmitoyl Tetrapeptide-7." An older INCI designation for the identical molecule — "Palmitoyl Tetrapeptide-3" — persists on product labels predating the Personal Care Products Council (PCPC) INCI renumbering. Finished cosmetic formulations may list either name, or both, depending on label vintage. The molecular weight is 694.9 daltons (PubChem CID 10078408) and the CAS registry number is 221227-05-0. Rigin, the trade material, is a mixture containing 500 ppm (0.05%) of the peptide, and the Cosmetic Ingredient Review took peptide use below 10 ppm as typical in finished cosmetics (Johnson et al., 2018).

Rigin is positioned in the Sederma catalogue as an "immunomodulating anti-inflammaging" peptide — distinct in mechanism from the firm's signal peptide Matrixyl® (palmitoyl pentapeptide-4 / pal-KTTKS), which is positioned as a pro-collagen signal peptide, and from Matrixyl synthe'6® (palmitoyl tripeptide-38), a later-generation signal peptide. Commercially, Rigin's most prominent role is as one of two peptides in Matrixyl® 3000 — a 1:1 combination of palmitoyl tripeptide-1 (pal-GHK) and palmitoyl tetrapeptide-7 (pal-GQPR) that Sederma markets as a complementary extracellular-matrix duo: palmitoyl tripeptide-1 as the pro-synthesis signal and palmitoyl tetrapeptide-7 as the anti-degradation / cytokine-attenuating partner. Matrixyl 3000 is one of the most widely used peptide complexes in mid- and upper-tier topical anti-aging skincare worldwide.

The intellectual framework the manufacturer uses to describe Rigin leans on two parallel biology traditions. The first is the longstanding literature on "tuftsin" and "rigin" as naturally occurring tetrapeptides liberated from IgG proteolysis that stimulate phagocyte activation and modulate cytokine signaling — a body of work going back to the 1970s and well summarized by Rocchi and colleagues in their synthesis and biological characterization of tuftsin and rigin analogues. The second is the "inflammaging" framework popularized by Franceschi and collaborators — the hypothesis that low-grade chronic elevation of pro-inflammatory cytokines, particularly IL-6 (a pro-inflammatory cytokine tied to chronic inflammation), drives age-related tissue dysfunction including collagen degradation in the skin. The Sederma positioning unifies these two traditions into a single marketing claim: an IgG-derived peptide that, topically, attenuates IL-6 secretion in the dermis and thereby protects the collagen-elastin matrix from cytokine-driven degradation. The underlying in-vitro signal is real; the leap from that signal to finished-product wrinkle claims is substantial, and is the basis of the "Limited Evidence" badge applied to this profile.

Mechanism of Action

Rigin's mechanistic claims rest on supplier data, which a 2021 review found mostly in patents and supplier brochures (Resende et al., 2021), plus older work on peptides cut from IgG antibodies (Rocchi et al., 1987). PubMed lists no independent replication of the supplier's skin-cell findings below.

• IL-6 attenuation in skin cells — Supplier data, as reviews summarize them, report that palmitoyl tetrapeptide-7 lowers IL-6 secretion by keratinocytes (Ferreira et al., 2020), including in a basal setting (Schagen, 2017). A review describes IL-6 as one of the main signaling pathways linking aging and chronic disease (Maggio et al., 2006).
• UVB-induced inflammation attenuation — The same reviews report that it reduces inflammation after ultraviolet-B (UVB) exposure (Schagen, 2017; Resende et al., 2021).
• Laminin and collagen VII stimulation — A 2021 review reports that it stimulates production of laminin IV and V and of collagen VII, citing work by Sederma scientists (Resende et al., 2021). PubMed lists no independent study of it.
• NF-κB (a master inflammation switch) pathway modulation (speculative) — No published study links palmitoyl tetrapeptide-7 to NF-κB; a 2020 review lists its molecular target as unknown (Ferreira et al., 2020).
• Tuftsin-like phagocyte activation — The parent GQPR sequence, called rigin, is a natural fragment of IgG (Johnson et al., 2018). In mouse peritoneal macrophages, rigin enhanced phagocytosis as much as tuftsin did (Rocchi et al., 1987).
• Palmitoylation for stratum corneum penetration — A 2021 review describes the hydrophobization of cosmetic peptides, such as adding a palmitic acid chain, as giving better penetration through the stratum corneum (Resende et al., 2021).
• Complementarity with palmitoyl tripeptide-1 (Matrixyl 3000) — Matrixyl 3000 pairs palmitoyl tripeptide-1, a signal peptide reported to raise collagen production (Errante et al., 2020), with palmitoyl tetrapeptide-7, whose reduction of IL-6 supplier information links to less inflammation-driven breakdown of the skin's matrix (Ferreira et al., 2020). Its human tests compared the blend with a placebo or excipient cream (Schagen, 2017; Johnson et al., 2018), so each peptide's share cannot be isolated.

What the Research Shows

The evidence base for Rigin / palmitoyl tetrapeptide-7 is unusually thin for a widely distributed cosmetic active. The ingredient has been in cosmetic circulation for roughly two decades and appears in hundreds of finished products worldwide, yet the peer-reviewed publication record specifically on the isolated peptide is dominated by manufacturer-supplied data, industry conference abstracts, and ingredient-review articles that reference those sources. What follows is the honest shape of the evidence.

• Manufacturer in-vitro data — Sederma's internal technical documentation (brochures and cosmetics-industry conference presentations) contains the core IL-6 attenuation and laminin / collagen VII stimulation data. These data are consistent across the multiple ingredient-review articles that cite them (Schagen 2017, Resende et al. 2021), but the underlying experiments were performed and analyzed by the manufacturer and have not been independently replicated in an adversarial peer-reviewed publication.
• Ingredient-review academic literature — Several review articles in the cosmetic-dermatology literature describe palmitoyl tetrapeptide-7's positioning and claimed mechanism. Lupo's 2005 review in Dermatologic Surgery (PMID 16029675) is the most widely cited early academic summary of cosmeceutical peptides including the palmitoyl-conjugate class. Schagen's 2017 open-access review in Cosmetics (MDPI; doi 10.3390/cosmetics4020016) is a more comprehensive treatment that explicitly summarizes Rigin's IL-6-attenuation positioning. Resende and colleagues (2021; PMID 34451799) reviewed synthetic peptide use in sensitive-skin cosmetics and summarized Rigin's mechanistic claims. These are summary articles — they catalogue manufacturer claims, they do not constitute independent clinical validation.
• Matrixyl 3000 as the closest finished-product evidence — Independent clinical evaluations of the Matrixyl 3000 combination (palmitoyl tripeptide-1 + palmitoyl tetrapeptide-7) exist in the cosmetic-dermatology literature. Because these studies invariably test the combination rather than the isolated peptides, they cannot by design separate Rigin's contribution from palmitoyl tripeptide-1's. Li and colleagues' 2023 evaluation in the Journal of Cosmetic Dermatology (doi 10.1111/jocd.15849) of a multi-peptide eye serum containing 4% Matrixyl 3000 is representative of the level of evidence — a small clinical evaluation reporting anti-wrinkle benefits for a multi-active formulation, unable to attribute effect to any individual peptide.
• Pal-KTTKS as the benchmark for what a positive cosmetic peptide study looks like — Robinson and colleagues at Procter & Gamble published a peer-reviewed vehicle-controlled clinical study of the related palmitoyl pentapeptide (a chain of 5 amino acids) pal-KTTKS (Matrixyl; PMID 18492182). That study — 93 women, 12 weeks, 3 ppm pal-KTTKS — reported improvements in photoaged facial skin on expert grading and image analysis. The relevant point for Rigin is contrastive: a cosmetic peptide can generate a defensible independent-or-semi-independent clinical publication, and the absence of such a study for isolated palmitoyl tetrapeptide-7 is conspicuous despite two decades of commercial availability.
• IgG-fragment and tuftsin background literature — The upstream biology of the GQPR sequence is well-characterized in the older immunology literature. Work by Rocchi and colleagues on the synthesis and biological activity of tuftsin and rigin derivatives documented phagocyte-activating and immunomodulatory properties of the naked peptides. This background establishes biological plausibility for an IgG-derived tetrapeptide having immune-modulating activity; it does not demonstrate that a palmitoylated analogue, applied topically at cosmetic concentration, produces meaningful skin benefits in humans.
• IL-6 and skin aging — the plausibility case — Independent literature robustly supports the proposition that IL-6 is a central cytokine in the aging process, both systemically and in skin-specific contexts where IL-6 elevation correlates with senescent fibroblast phenotype and altered extracellular matrix turnover. Maggio and colleagues' review of IL-6 in aging and chronic disease (PMID 16799139) is one representative source. This literature establishes that attenuating IL-6 in the skin is a defensible anti-aging target; it does not demonstrate that topical Rigin achieves that attenuation at clinically relevant concentrations in human skin.
• Topical peptide penetration — Peptide penetration of the stratum corneum is generically limited, and the palmitoyl conjugation strategy is well-documented for improving partition and transport. Reviews of topical anti-aging peptide delivery (Gorouhi & Maibach 2009, PMID 19570099; Zhang & Falla 2009, PMID 19695481) summarize the state of the art for getting peptide actives into the viable epidermis. The evidence for palmitoyl conjugates passing the stratum corneum in ex-vivo models is reasonable; the evidence that specifically palmitoyl tetrapeptide-7 reaches concentrations sufficient for the IL-6 attenuation demonstrated in cell culture is an extrapolation.
• Formulation-level synergy claims — Matrixyl 3000 proponents describe synergistic combination benefits between pal-GHK and pal-GQPR in finished cosmetics. Formulation-synergy claims at the cosmetic-industry level are typical and typically underpowered — small-n clinical evaluations on finished multi-active products are interpreted as combination evidence without the factorial design required to test synergy rigorously. This is a generic weakness of cosmetic clinical evidence, not a Rigin-specific indictment.
• Public-interest and consumer signal — In a survey of 280 anti-aging products from more than 40 multinational brands sold in Portugal in 2011 and 2018, palmitoyl tetrapeptide-7 was the most used peptide, ahead of palmitoyl oligopeptide and acetyl hexapeptide-8 (Argireline) (Ferreira et al., 2020), and industry had reported 249 cosmetic uses of it to the FDA's voluntary registration program by 2014 (Johnson et al., 2018). Consumer-facing popularity does not validate mechanism or efficacy.

Human Data

Human data specifically on isolated Rigin / palmitoyl tetrapeptide-7 is, to a first approximation, absent from the peer-reviewed literature. This section honestly inventories what exists, what is adjacent, and what is not available.

• No independent RCT of isolated Rigin — A PubMed search for "palmitoyl tetrapeptide-7" or "palmitoyl tetrapeptide-3" or "Pal-GQPR" as a cosmetic clinical trial endpoint returns no double-blind vehicle-controlled RCT of the isolated peptide published in a peer-reviewed journal. Manufacturer data, as reviews summarize them, describe a randomized controlled study with gains in skin elasticity, firmness and softness (Ferreira et al., 2020), and a supplier study of 3% Matrixyl 3000 cream on half the face of 24 volunteers for two months reported fewer deep wrinkles than at the start (Johnson et al., 2018); both come from supplier documents, not peer-reviewed papers.
• Matrixyl 3000 combination evaluations — The Matrixyl 3000 combination (palmitoyl tripeptide-1 + palmitoyl tetrapeptide-7) has been evaluated in small finished-product studies typically conducted by manufacturers or formulators. These are not isolatable to Rigin's contribution, and most are industry-sponsored.
• Multi-peptide finished-serum clinical evaluations — Li et al., 2023 (J Cosmet Dermatol; doi 10.1111/jocd.15849), evaluated a commercial multi-peptide eye serum containing 10% Argireline (acetyl hexapeptide-8), 4% Matrixyl 3000 (palmitoyl tetrapeptide-7 + palmitoyl tripeptide-1), and 2% Eyeliss (dipeptide-2 + palmitoyl tetrapeptide-7 + hesperidin methyl chalcone). The study reported wrinkle-depth and firmness improvements versus baseline over a treatment period. The design cannot attribute effect to palmitoyl tetrapeptide-7 or to any individual active. This is the closest published "human data" the ingredient has — a multi-active finished-product evaluation in which Rigin is one of several peptides.
• Adjacent cosmetic peptide RCT — pal-KTTKS (Matrixyl) — Robinson et al., 2005 (PMID 18492182). Randomized, double-blind, vehicle-controlled split-face study in 93 Caucasian women aged 35–55, 12 weeks. 3 ppm pal-KTTKS provided statistically significant improvement in wrinkles and fine lines versus vehicle on technical and expert-grader image analysis. This is the high-water mark for independent-or-semi-independent cosmetic peptide clinical evidence, and it is for the sister compound pal-KTTKS — not for pal-GQPR.
• Adjacent cosmetic peptide publication — acetyl hexapeptide-8 (Argireline) — Blanes-Mira et al., 2002 (PMID 18498523). The foundational characterization of acetyl hexapeptide-8 with in-vitro and preliminary topical human data for wrinkle reduction. Again, this is adjacent — a different cosmetic peptide with a different mechanism — but it is a reference case for what an independent peer-reviewed cosmetic peptide evaluation looks like.
• Adjacent clinical review — peptide cosmeceuticals — Lupo, 2005 (PMID 16029675) — the most commonly cited academic review cataloguing cosmeceutical peptides including palmitoyl-conjugate signal peptides and immunomodulatory peptides. Lupo's review references manufacturer claims rather than primary RCT data for Rigin.
• IgG-derived peptide immunomodulation — Older immunology literature characterizes naked GQPR and related IgG-derived peptides (including tuftsin, Thr-Lys-Pro-Arg) as modulators of phagocyte activity in isolated cell systems; the rigin work used mouse macrophages (Rocchi et al., 1987). This is cell data rather than clinical RCT data — foundational biology, not efficacy evidence for a topical anti-aging product.
• IL-6 and skin senescence — The broader literature on IL-6 as a marker and driver of dermal fibroblast senescence (Maggio et al., 2006, PMID 16799139; Franceschi et al., 2018, PMID 30046148) establishes the plausibility of an IL-6-attenuating topical intervention. Plausibility is not efficacy evidence.
• Safety / pharmacovigilance — Rigin / palmitoyl tetrapeptide-7 has been in commercial cosmetic use for roughly two decades in many jurisdictions. Post-market safety signals are minimal — occasional contact sensitization reports of the kind expected for any cosmetic active, no reproducible systemic toxicity signal, no notable regulatory enforcement action. The Cosmetic Ingredient Review concluded it is safe in cosmetics at present use levels (Johnson et al., 2018); that is a finding about safety, not evidence that it works.

Reconstitution & Storage

Rigin is not reconstituted the way a freeze-dried research peptide is: Sederma sells it as a ready-made mixture containing 500 ppm palmitoyl tetrapeptide-7, which formulators add to finished cosmetics (Johnson et al., 2018).

• Compatibility — Formulation guides describe keeping high-concentration ascorbic acid at low pH and benzoyl peroxide out of the same phase.
• Heat sensitivity — Formulation guides describe adding Rigin at the cool-down phase, after the emulsion forms, rather than during heating.
• pH sensitivity — Formulation guides describe keeping finished-product pH within Sederma's stated range of 5.0–7.0.
• Not an injectable or research-peptide product — Rigin is a cosmetic raw material, and its safety review covers cosmetic use only (Johnson et al., 2018).

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Side Effects & Risks

The Cosmetic Ingredient Review's expert panel concluded that palmitoyl tetrapeptide-7 is safe in cosmetics in the present practices of use and concentration, citing low use concentrations and negative safety tests; for this peptide, the tests were run on Rigin: a repeated patch test, a bacterial mutation (Ames) test, which was negative, and a hen's-egg eye test (Johnson et al., 2018).

• Contact sensitization — In a repeated-insult patch test of Rigin (500 ppm palmitoyl tetrapeptide-7) in 52 healthy adults aged 18–79, the results did not indicate a potential for allergic contact sensitization (Johnson et al., 2018).
• No systemic safety data — The Cosmetic Ingredient Review's report gives no absorption data for palmitoyl tetrapeptide-7, and it found no published carcinogenicity data (Johnson et al., 2018).
• Irritation — The same patch test did not indicate a potential for skin irritation (Johnson et al., 2018).
• Ocular exposure — In a hen's-egg membrane test of eye irritation, Rigin was classed as slightly irritating (Johnson et al., 2018).
• Pregnancy and lactation — The Cosmetic Ingredient Review found no published reproductive or developmental toxicity data on palmitoyl tetrapeptide-7 (Johnson et al., 2018). Consult a licensed healthcare provider.
• Pediatric use — PubMed lists no study of it in children.
• Drug interactions — Not characterized; PubMed lists no interaction study.
• Allergenicity of the IgG-derived sequence — The GQPR sequence is a natural fragment of IgG antibodies (Johnson et al., 2018). Its allergy potential has been tested in one repeated patch test of Rigin, described above (Johnson et al., 2018).
• Regulatory posture — In the US, cosmetic products and ingredients other than color additives need no FDA approval before sale (FDA); the EU's CosIng register lists palmitoyl tetrapeptide-7 as a skin-conditioning ingredient with no annex restriction.

Bloodwork & Monitoring

No trial, label or guideline sets bloodwork or monitoring for palmitoyl tetrapeptide-7. The human tests in its safety review measured the skin: patch-test reactions to Rigin in 52 adults, and wrinkles, roughness and elasticity in 24 volunteers using a 3% Matrixyl 3000 cream (Johnson et al., 2018).

Commonly Stacked With

Besides Rigin itself, palmitoyl tetrapeptide-7 is sold in Sederma blends: with palmitoyl tripeptide-1 in Matrixyl 3000 and Haloxyl, and with dipeptide-2 in Eyeliss (Ferreira et al., 2020).

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Legal Status

Related Compounds

Cosmetic peptides in the matrikine and cytokine-attenuation class:

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References

1. Blanes-Mira C, Clemente J, Jodas G, Gil A, Fernández-Ballester G, Ponsati B, Gutierrez L, Pérez-Payá E, Ferrer-Montiel A. A synthetic hexapeptide (Argireline) with antiwrinkle activity. Int J Cosmet Sci. 2002;24(5):303-310. PMID: 18498523. (Foundational cosmetic peptide characterization methodology — reference for the class of acetyl / palmitoyl cosmeceutical peptide assessment.)
2. Robinson LR, Fitzgerald NC, Doughty DG, Dawes NC, Berge CA, Bissett DL. Topical palmitoyl pentapeptide provides improvement in photoaged human facial skin. Int J Cosmet Sci. 2005;27(3):155-160. PMID: 18492182. (The reference independent-style clinical study for a palmitoylated cosmetic peptide — sister compound pal-KTTKS / Matrixyl, not pal-GQPR.)
3. Lupo MP. Cosmeceutical peptides. Dermatol Surg. 2005;31(7 Pt 2):832-836; discussion 836. PMID: 16029675. (Widely cited academic review of the cosmeceutical peptide class including signal peptides, neurotransmitter-acting peptides, and carrier peptides.)
4. Lupo MP, Cole AL. Cosmeceutical peptides. Dermatol Ther. 2007;20(5):343-349. PMID: 18045359. (Follow-up review summarizing the three main categories of cosmeceutical peptides with references to Rigin / palmitoyl tetrapeptide-7 class claims.)
5. Schagen SK. Topical Peptide Treatments with Effective Anti-Aging Results. Cosmetics. 2017;4(2):16. doi:10.3390/cosmetics4020016. (Open-access comprehensive cosmeceutical peptide review covering palmitoyl tetrapeptide-7 / Rigin positioning and IL-6 attenuation claims.)
6. Ferreira MS, Magalhães MC, Sousa Lobo JM, Almeida IF. Trending Anti-Aging Peptides. Cosmetics. 2020;7(4):91. doi:10.3390/cosmetics7040091. (Review of the current cosmetic peptide landscape with detailed discussion of palmitoyl tetrapeptide-7 mechanism claims.)
7. Resende DISP, Ferreira MS, Sousa-Lobo JM, Sousa E, Almeida IF. Usage of Synthetic Peptides in Cosmetics for Sensitive Skin. Pharmaceuticals (Basel). 2021;14(8):702. PMID: 34451799. (Review of cosmetic peptide use in sensitive-skin formulations, with mechanistic discussion of palmitoyl tetrapeptide-7's IL-6 attenuation and inflammation-response dampening claims.)
8. Secchi G. Role of protein in cosmetics. Clin Dermatol. 2008;26(4):321-325. PMID: 18691510. (Background on protein and peptide cosmetic ingredient class.)
9. Gorouhi F, Maibach HI. Role of topical peptides in preventing or treating aged skin. Int J Cosmet Sci. 2009;31(5):327-345. PMID: 19570099. (Cosmetic peptide topical-delivery review — stratum corneum penetration, palmitoyl conjugate strategy, and mechanism-by-mechanism evidence inventory.)
10. Zhang L, Falla TJ. Cosmeceuticals and peptides. Clin Dermatol. 2009;27(5):485-494. PMID: 19695481. (Cosmeceutical peptide review discussing palmitoyl tetrapeptide-7 positioning within the signal / neurotransmitter / carrier peptide framework.)
11. Maggio M, Guralnik JM, Longo DL, Ferrucci L. Interleukin-6 in aging and chronic disease: a magnificent pathway. J Gerontol A Biol Sci Med Sci. 2006;61(6):575-584. PMID: 16799139. (Foundational review of IL-6 in aging — the biological plausibility case for Rigin's anti-inflammaging positioning.)
12. Franceschi C, Garagnani P, Parini P, Giuliani C, Santoro A. Inflammaging: a new immune-metabolic viewpoint for age-related diseases. Nat Rev Endocrinol. 2018;14(10):576-590. PMID: 30046148. (Inflammaging framework citation — the broader biological context for cosmetic anti-inflammaging peptide claims.)
13. Rocchi R, Biondi L, Filira F, Gobbo M, Dagan S, Fridkin M. Synthesis and biological activity of tuftsin and rigin derivatives containing monosaccharides or monosaccharide derivatives. Int J Pept Protein Res. 1987;29(2):250-261. PMID: 3570666. (Classic synthesis and biological characterization of naked tuftsin and rigin tetrapeptides from the IgG hinge region — foundational biology for the Sederma palmitoyl-conjugate product.)
14. Najjar VA, Nishioka K. "Tuftsin": a natural phagocytosis stimulating peptide. Nature. 1970;228(5272):672-673. PMID: 4097539. (Origin-of-the-family reference — the IgG-hinge tuftsin literature that underpins the broader rigin-class biology.)
15. Li H, Colombo I, Tetteh-Quarcoo V, et al. Clinical evidence of the efficacy and safety of a new multi-peptide anti-aging topical eye serum. J Cosmet Dermatol. 2023;22(8):2164-2174. doi:10.1111/jocd.15849. (Representative multi-peptide finished-product clinical evaluation including Matrixyl 3000 [palmitoyl tripeptide-1 + palmitoyl tetrapeptide-7] at 4% — nearest-neighbor human data, combination-only.)
16. Hoppel M, Reznicek G, Kählig H, Kotisch H, Resch GP, Valenta C. Topical delivery of acetyl hexapeptide-8 from different emulsions: Influence of emulsion composition and internal structure. Eur J Pharm Sci. 2015;68:27-35. PMID: 25497319. (Methodologically adjacent cosmetic peptide skin-penetration study — relevant for the generic topical-delivery case for palmitoylated and acetylated cosmetic peptides.)
17. Katayama K, Armendariz-Borunda J, Raghow R, Kang AH, Seyer JM. A pentapeptide from type I procollagen promotes extracellular matrix production. J Biol Chem. 1993;268(14):9941-9944. PMID: 8486721. (Origin-of-the-family reference for pal-KTTKS / Matrixyl — the sister palmitoyl cosmetic peptide with which Rigin is routinely combined.)
18. Fields K, Falla TJ, Rodan K, Bush L. Bioactive peptides: signaling the future. J Cosmet Dermatol. 2009;8(1):8-13. PMID: 19250159. (Cosmetic bioactive peptide overview covering palmitoyl tetrapeptide-7 class and combination formulation logic.)
19. Errante F, Ledwoń P, Latajka R, Rovero P, Papini AM. Cosmeceutical Peptides in the Framework of Sustainable Wellness Economy. Front Chem. 2020;8:572923. PMID: 33195061. (Cosmetic peptide overview referencing palmitoyl tetrapeptide-7 within the broader framework of synthetic cosmetic actives.)
20. Reddy BY, Jow T, Hantash BM. Bioactive oligopeptides in dermatology: Part I. Exp Dermatol. 2012;21(8):563-568. PMID: 22672743. (Review of bioactive oligopeptides in dermatology including cosmetic palmitoyl-conjugate peptides.)
21. FDA. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (503A categories list), versions updated April 15, April 22 and May 14, 2026. fda.gov/media/94155/download. Read October 3, 2026. (Notice that 12 peptides would leave Category 2 because their nominations were withdrawn; their removal; GHK-Cu, except injectable, back in Category 1.)
22. Johnson W Jr, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler DC, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Gill LJ, Heldreth B. Safety Assessment of Tripeptide-1, Hexapeptide-12, Their Metal Salts and Fatty Acyl Derivatives, and Palmitoyl Tetrapeptide-7 as Used in Cosmetics. Int J Toxicol. 2018;37(3 suppl):90S-102S. doi:10.1177/1091581818807863. Cosmetic Ingredient Review final report, released June 30, 2014: cir-safety.org/sites/default/files/tripep062014final.pdf. Read October 4, 2026. (The Cosmetic Ingredient Review expert panel's safety assessment: Rigin contains 500 ppm palmitoyl tetrapeptide-7; typical peptide use under 10 ppm; patch, eye and Ames tests on Rigin; a 3% Matrixyl 3000 cream study.)

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