Pal-AHK
A palmitoylated cosmeceutical tripeptide (Ala-His-Lys) studied for hair growth stimulation via dermal papilla cell proliferation and anti-apoptotic signaling, as well as collagen synthesis and skin rejuvenation.
What is Pal-AHK?
Pal-AHK is a synthetic lipopeptide consisting of the tripeptide alanine-histidine-lysine (AHK) conjugated to palmitic acid. Its molecular formula is C31H56N6O5 with a molecular weight of approximately 592.8 Da. The palmitoyl modification enhances lipophilicity, improving penetration through the skin's lipid-rich stratum corneum compared to the unmodified AHK sequence. While structurally related to Pal-GHK (Palmitoyl Tripeptide-1) — which uses glycine in place of alanine — Pal-AHK has a distinct research profile centered on hair follicle stimulation and dermal papilla cell survival rather than matrikine-driven collagen signaling. The AHK sequence also has affinity for copper ions, forming the AHK-Cu complex (Copper Tripeptide-3), which is the form used in most published in vitro research. Its INCI name is Palmitoyl Tripeptide-28, though it is also referenced under the older designation Palmitoyl Tripeptide-3.
What Pal-AHK Is Investigated For
Pal-AHK is a palmitoylated cosmeceutical tripeptide marketed primarily for hair growth stimulation (via dermal papilla cell proliferation and anti-apoptotic signaling), collagen synthesis and skin anti-aging, and — with weaker grounding — for skin pigmentation and tone improvement. The strongest signal, such as it is, comes from a single in vitro and ex vivo study (Pyo et al., 2007) using the copper-complexed form AHK-Cu on cultured human hair follicles and dermal papilla cells, showing follicle elongation, elevated Bcl-2/Bax ratio, reduced caspase-3 and PARP cleavage, and VEGF upregulation with TGF-β1 suppression. No published human clinical trials exist for Pal-AHK or AHK-Cu for any endpoint, no in vivo animal hair-growth studies have been completed, and whether the palmitoylated form retains the biological activity demonstrated for the copper complex is assumed rather than demonstrated. Pigmentation claims have no peer-reviewed mechanistic support. For androgenetic alopecia, FDA-approved minoxidil and finasteride have an incomparably stronger evidence base.
History & Discovery
The AHK tripeptide (Ala-His-Lys) sits within the broader copper-tripeptide family that includes the much better-studied GHK (Gly-His-Lys), the original copper-binding peptide identified by Loren Pickart in human plasma in the 1970s. Researchers exploring copper-tripeptide structure-activity relationships found that AHK retained copper-binding capacity through its histidine-imidazole and lysine-amine groups while showing a distinct biological activity profile centered on hair follicle and dermal papilla cell biology rather than the matrikine-like collagen signaling associated with GHK-Cu. The key foundational study was published by Pyo and colleagues in 2007, demonstrating that AHK-Cu (the copper-complexed form, also designated copper tripeptide-3) stimulated human hair follicle elongation ex vivo and dermal papilla cell proliferation in vitro at picomolar to nanomolar concentrations, with anti-apoptotic molecular signatures (elevated Bcl-2/Bax ratio, reduced cleaved caspase-3 and PARP). This single study has driven most subsequent commercial interest in the peptide for hair-loss formulations. The palmitoylated form (Pal-AHK, INCI palmitoyl tripeptide-28, also referenced under the older designation palmitoyl tripeptide-3) was developed for improved transdermal delivery in cosmeceutical formulations, following the same lipidation strategy used for Pal-GHK and the Matrixyl-family matrikines. Independent peer-reviewed replication of the hair-growth findings remains thin, and no published human clinical trials for Pal-AHK or AHK-Cu specifically have been completed.
How It Works
Pal-AHK works primarily by supporting hair follicle cells. In lab studies, the AHK sequence (in its copper-bound form) stimulated dermal papilla cells — the specialized cells at the base of hair follicles that control the growth cycle — to proliferate and survive longer. It does this by tipping the balance of survival proteins: increasing Bcl-2 (a pro-survival signal) and decreasing Bax (a pro-death signal), which reduces programmed cell death. It also boosts VEGF production, which promotes blood vessel formation and nutrient delivery to follicles and skin. Separately, AHK stimulates fibroblasts to produce more collagen type I, contributing to skin firmness. The palmitoyl modification helps the peptide penetrate the skin's outer lipid barrier when applied topically.
The AHK tripeptide (L-alanyl-L-histidyl-L-lysine), particularly in its copper-complexed form (AHK-Cu), exerts biological effects through multiple pathways in dermal papilla cells (DPCs) and fibroblasts. In the key study by Pyo et al. (2007), AHK-Cu at concentrations of 10^-12 to 10^-9 M stimulated human hair follicle elongation ex vivo and DPC proliferation in vitro. At the molecular level, AHK-Cu elevated the Bcl-2/Bax ratio — upregulating the anti-apoptotic protein Bcl-2 while downregulating the pro-apoptotic protein Bax — and reduced cleaved caspase-3 by 42.7% and cleaved PARP by 77.5% at 10^-9 M, demonstrating potent anti-apoptotic activity in DPCs. In dermal fibroblasts, AHK-Cu stimulated proliferation, elevated VEGF secretion (supporting angiogenesis and follicular vascularization), and decreased TGF-beta1 secretion. TGF-beta1 is a known catagen-inducing factor that suppresses hair growth; its reduction may create a more favorable environment for sustained anagen-phase activity. Collagen type I production was reported to increase up to 300% compared to controls in fibroblast cultures. The palmitoyl moiety (C16 fatty acid) conjugated to the N-terminus enhances lipophilicity and transdermal penetration through the stratum corneum, similar to the palmitoylation strategy used in Pal-GHK and other cosmeceutical peptides. Whether the palmitoylated form is cleaved to release free AHK intracellularly or acts as an intact molecule at the cell surface remains uncharacterized.
Evidence Snapshot
Human Clinical Evidence
No published human clinical trials exist for Pal-AHK or AHK-Cu specifically. Cosmeceutical products containing Pal-AHK are commercially available and widely used, providing indirect tolerability evidence, but no controlled clinical data on efficacy for hair growth, pigmentation, or anti-aging outcomes has been published in peer-reviewed literature.
Animal / Preclinical
Limited but notable. The foundational study (Pyo et al., 2007; PMID: 17703734) demonstrated AHK-Cu stimulated human hair follicle elongation ex vivo and dermal papilla cell proliferation in vitro, with clear anti-apoptotic molecular signatures (elevated Bcl-2/Bax, reduced caspase-3 and PARP). Fibroblast studies showed increased VEGF, reduced TGF-beta1, and up to 300% collagen type I increase. Sadgrove et al. (2021) discussed AHK in the context of dual-acting cosmeceutical peptides for hair and skin. No in vivo animal hair growth studies have been published.
Mechanistic Rationale
Moderate. The anti-apoptotic mechanism in DPCs is well-characterized at the protein level (Bcl-2/Bax, caspase-3, PARP). VEGF upregulation and TGF-beta1 suppression are mechanistically consistent with hair growth promotion. Collagen stimulation in fibroblasts is documented. However, the pathway between the palmitoylated form and these cellular effects is assumed rather than demonstrated, and no receptor-level binding data exists.
Research Gaps & Open Questions
What the current literature has not yet settled about Pal-AHK:
- 01Human clinical trials — no published controlled human trials exist for Pal-AHK or AHK-Cu for hair growth, skin pigmentation, anti-aging, or any other endpoint. All biological activity claims rest on preclinical in vitro and ex vivo work.
- 02Independent replication of the foundational Pyo et al. 2007 hair-growth study — most current commercial claims trace back to a single research group's findings, and independent peer-reviewed replication is essential before treating the mechanism as established.
- 03Whether the palmitoylated form (Pal-AHK) retains the biological activity demonstrated for the copper-complexed form (AHK-Cu) at the cellular level — this is assumed but not directly characterized.
- 04In vivo animal hair-growth studies — no published rodent or other in vivo hair-growth models have been completed for AHK-family peptides, which is a notable gap given the strength of in vitro and ex vivo claims.
- 05Real-world skin and scalp penetration quantification across commercial formulations — delivery to dermal papilla cells, fibroblasts, or melanocytes from typical topical products is poorly characterized.
- 06Safety profile under chronic use, particularly for scalp formulations applied long-term — no formal safety surveillance data exists, and the chronic copper-coordination biology of the AHK-Cu form has not been studied for long-term cumulative effects.
- 07Mechanistic basis for marketed pigmentation and skin-tone claims — no peer-reviewed published research directly demonstrates Pal-AHK or AHK-Cu effects on melanogenesis or melanocyte biology; pigmentation marketing claims are commercially driven rather than evidence-based.
Forms & Administration
Pal-AHK is used exclusively as a topical cosmeceutical ingredient. It is typically formulated in serums, creams, and scalp treatments targeting hair growth or skin anti-aging. Concentrations in commercial products are generally not standardized or disclosed. The copper-complexed form (AHK-Cu) is also available as a topical research compound. No injectable formulations have been studied in humans. Topical cosmeceutical use does not require a prescription.
Dosing & Protocols
The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.
Typical Range
Cosmetic and scalp formulations typically include Pal-AHK at concentrations that are not standardized or commonly disclosed on labels — manufacturer guidance varies, and finished products commonly use anywhere from 0.05% to 2% depending on formulation strategy. There is no published clinical dose-finding data in humans for either Pal-AHK or AHK-Cu. The foundational in vitro work used the copper-complexed form at picomolar to nanomolar concentrations against cultured cells, which does not translate directly to a topical product percentage.
Frequency
Applied topically once or twice daily to scalp (for hair-loss formulations) or facial skin (for anti-aging formulations). There are no published clinical trial protocols defining a standard application frequency in humans.
Timing Considerations
No specific timing requirements: can be administered at any time of day, with or without food, and is not tied to exercise timing. Consistency matters more than the specific clock — dose at roughly the same time each day (or same day each week, for weekly protocols) to keep exposure steady.
Cycle Length
Continuous indefinite use is the typical commercial use pattern. Like other cosmeceutical signal peptides, any biological effect requires sustained application — the mechanism is not designed for cycling, and benefit (where present) recedes with discontinuation.
Protocol Notes
The palmitoyl modification is the formulation choice that distinguishes Pal-AHK from a bare tripeptide or copper complex. Palmitic acid conjugation improves partition into the lipid-rich stratum corneum, which is where a small charged tripeptide alone would stall. An important and underappreciated caveat: most of the published mechanistic data on AHK comes from the copper-complexed form (AHK-Cu), and it is assumed — but not directly demonstrated — that Pal-AHK is cleaved or otherwise behaves equivalently to AHK-Cu once it reaches target cells. Whether the palmitoylated form retains the same anti-apoptotic and VEGF-modulating activities at the cellular level has not been characterized. Pal-AHK is commonly co-formulated with other peptides in 'multi-peptide' anti-aging or hair-growth products: Pal-GHK / GHK-Cu (chemically related copper tripeptide), Matrixyl-family matrikines, Pal-AHK alongside Pal-GQPR for hair formulations, and biotin or caffeine in scalp products. Head-to-head clinical evidence supporting multi-peptide stacks over single-peptide products is essentially absent for this peptide family. Injectable AHK or Pal-AHK is not an established category in humans. Some scalp mesotherapy and microneedling protocols introduce copper-tripeptide formulations into superficial dermis, but published efficacy and safety data for Pal-AHK in this context is absent.
Pal-AHK is a cosmetic ingredient, not a drug. It is not FDA-approved to treat hair loss, skin aging, or any other medical condition. Cosmetic claims permitted on labels are limited to appearance-related language. For androgenetic alopecia, FDA-approved options (topical minoxidil, oral finasteride) have a far stronger evidence base than any cosmetic peptide.
Timeline of Effects
Onset
No published clinical trial timelines exist for Pal-AHK in humans. By analogy with other cosmetic peptides and with hair-cycle biology, any plausible hair-related effects would require months of sustained application before becoming visible (hair follicles cycle on a timescale of months to years). Skin-related effects from collagen-stimulating components, where present, would be expected on the same 8–12 week timescale as other matrikine-class peptides.
Peak Effect
Unknown — no published peak-effect timing exists for Pal-AHK. In vitro work establishes biological activity in cell culture and ex vivo follicles; translation to any human time-course is speculative.
After Discontinuation
Unknown for Pal-AHK specifically. By analogy with other cosmeceutical peptides, any biological effect would be expected to recede after discontinuation as the signaling input is withdrawn, with hair-cycle effects following the slow timescale of natural follicle turnover.
Common Questions
Who Pal-AHK Is NOT For
- •Broken, irritated, or actively inflamed scalp or skin — wait until the barrier is intact before applying cosmetic peptide formulations; application to compromised skin increases irritation potential.
- •Known hypersensitivity to Pal-AHK, copper tripeptides, or to other components of the cosmetic vehicle (preservatives, fragrances, emulsifiers); contact dermatitis is uncommon but reported.
- •Pregnancy and breastfeeding — topical cosmetic use on intact skin is generally considered low-risk, but there is no dedicated safety data in pregnancy, and a conservative default is to minimize biologically active peptide use during this window.
- •Pediatric use — no data and no clinical reason for children or adolescents to use anti-aging or hair-growth peptides.
- •Wilson's disease or other disorders of copper metabolism — although topical exposure to copper from a tripeptide complex is minimal, patients with copper-handling disorders should consult a clinician before using copper-tripeptide formulations.
- •Do not inject cosmetic Pal-AHK preparations — these are not sterile injectable products and there is no clinical or safety basis for injection in humans.
Drug & Supplement Interactions
Documented pharmacological drug interactions for topical Pal-AHK are minimal. Systemic absorption from typical topical use is low, and the palmitoylated tripeptide is not expected to reach clinically relevant plasma levels or interact with oral or injected medications. The relevant interaction space is topical layering. Pal-AHK is generally compatible with other cosmetic actives — niacinamide, hyaluronic acid, peptides, and gentle scalp tonics layer readily. Co-formulation with other copper tripeptides (GHK-Cu, Pal-GHK) is common, though there is a theoretical concern that competing copper-binding peptides could interfere with each other's copper coordination — clinical relevance unclear. Pairing with topical minoxidil in scalp routines is common in over-the-counter hair-growth product designs; no specific interaction has been documented but the combination is not formally studied. High-concentration L-ascorbic acid (vitamin C) and strong AHA/BHA exfoliants may destabilize peptide actives if applied in the same layer or immediately after, so spacing to different times of day is sensible. For hair-loss patients on FDA-approved therapies (oral finasteride, oral minoxidil, dutasteride), there is no documented interaction with Pal-AHK at the level of topical cosmetic exposure, but Pal-AHK should not be relied on as a substitute for evidence-based pharmacologic options.
Safety Profile
Common Side Effects
Cautions
- • Not FDA-approved as a drug — marketed as a cosmeceutical ingredient
- • Injectable use has not been studied in humans
- • Most published research used the copper-complexed form (AHK-Cu), not the palmitoylated form
- • Quality and concentration vary across cosmeceutical and research-grade sources
- • No established dosing guidelines for any route of administration
What We Don't Know
Systemic safety has not been evaluated. Long-term topical safety is inferred from general cosmeceutical use but not supported by formal clinical safety trials. Whether the palmitoylated form retains the same biological activity as the copper-complexed form in vivo has not been directly confirmed. The effects on melanogenesis and hair pigmentation lack published mechanistic data.
Legal Status
United States
Regulated as a cosmetic ingredient under FDA cosmetic law, not as a drug. Over-the-counter sale in finished cosmetic formulations is permitted without prescription. Palmitoyl tripeptide-28 (and the older designation palmitoyl tripeptide-3) is INCI-listed and appears in cosmeceutical hair and skin products. Not approved as a drug for hair loss, skin aging, or any other medical indication — labels are limited to cosmetic appearance claims. Hair-loss claims that cross into drug-claim territory ('treats alopecia,' 'reverses balding') are not permitted on cosmetic labels.
International
Permitted as a cosmetic ingredient across the EU (CosIng database), UK, Canada, Australia, Japan, and most major markets. Cosmetic ingredient safety reviews of related copper tripeptides and palmitoyl tripeptides have not raised concerns at typical formulation levels.
Sports & Competition
Not listed on the WADA Prohibited List and not a realistic doping concern. Topical cosmetic peptides have negligible systemic exposure relevant to performance.
Regulatory status changes over time. Verify current local rules with a qualified professional.
Myths & Misconceptions
Myth
Pal-AHK is clinically proven to grow hair.
Reality
It is not. The hair-growth evidence consists of a single in vitro and ex vivo study using the copper-complexed form (AHK-Cu), not the palmitoylated form, and not in any human clinical trial. No controlled human trials have been published for Pal-AHK or AHK-Cu for hair growth. The peptide is biologically interesting at the preclinical level but unproven in clinical settings. For androgenetic alopecia, FDA-approved options (minoxidil, finasteride) have a far stronger evidence base.
Myth
Pal-AHK and Pal-GHK are essentially the same peptide.
Reality
Both are palmitoylated copper-binding tripeptides with histidine-lysine motifs, but they differ at the first amino acid (alanine vs. glycine) and have distinct research profiles. Pal-GHK is the well-studied matrikine collagen-stimulating peptide; Pal-AHK is the less-studied dermal papilla / hair follicle-focused peptide. They are complementary in product designs but are not interchangeable — and the much weaker evidence base for AHK should not be conflated with GHK's better-developed literature.
Myth
Because Pal-AHK is a copper peptide relative, it has all the well-documented anti-aging effects of GHK-Cu.
Reality
AHK-Cu and GHK-Cu share copper-binding capacity but engage distinct biological pathways. The matrikine collagen-stimulation literature is essentially all GHK-based. Treating Pal-AHK as a substitute for GHK-Cu's documented anti-aging activity overstates what the AHK-specific evidence actually supports.
Myth
Pal-AHK improves skin pigmentation and reduces age spots.
Reality
This claim appears in commercial cosmeceutical marketing for some Pal-AHK products but has no peer-reviewed published research directly demonstrating effects on melanogenesis or melanocyte biology. For evidence-based pigmentation reduction, established actives (Decapeptide-12, niacinamide, vitamin C, tranexamic acid, hydroquinone) have a far stronger basis.
Myth
Pal-AHK is safe to inject for stronger hair-growth effect.
Reality
Cosmetic Pal-AHK preparations are not sterile injectable products, not manufactured under injectable standards, and there is no authorized injectable category for human use. Injecting cosmetic peptide products carries documented infection risk, and there is no clinical efficacy data supporting injection over topical application.
Published Research
3 studiesTopical and nutricosmetic products for healthy hair and dermal antiaging using "dual-acting" (2 for 1) plant-based peptides, hormones, and cannabinoids
Sadgrove et al. (2021) review discussing AHK among dual-acting cosmeceutical peptides for hair and skin, contextualizing its TGF-beta modulation and potential for combined dermal and follicular benefits.
The effect of tripeptide-copper complex on human hair growth in vitro
Foundational study by Pyo et al. (2007) demonstrating AHK-Cu stimulates human hair follicle elongation ex vivo and dermal papilla cell proliferation in vitro, with anti-apoptotic effects via Bcl-2/Bax modulation and reduced caspase-3/PARP cleavage.
Usage of Synthetic Peptides in Cosmetics for Sensitive Skin
Comprehensive review of synthetic peptides in cosmeceuticals including palmitoyl tripeptides, covering mechanisms, skin penetration enhancement via lipidation, and safety profiles.
Quick Facts
- Class
- Cosmeceutical Peptide
- Tier
- D
- Evidence
- Preliminary
- Safety
- Limited Data
- Updated
- Apr 2026
- Citations
- 3PubMed
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Clinical Trials
View Clinical TrialsLinks to ClinicalTrials.gov for reference. Listing does not imply endorsement.