Peptides for skin fall into two very different groups: copper peptides such as GHK-Cu and AHK-Cu, sold mainly in creams and serums for aging skin and hair, and tanning peptides such as Melanotan II, sold as unapproved injections and nasal sprays. GHK-Cu boosts collagen in lab studies, but human evidence is small,[1][4] while Melanotan II has been linked to changing moles and melanoma in case reports.[14]

This overview explains what skin peptides are, how they work, what human trials found, the difference between topical and injected use, and the legal and safety picture in 2026.

What are peptides for skin?

Peptides are short chains of amino acids. In skincare, the term usually means small signaling peptides added to creams to support collagen or the skin barrier. GHK, for example, is a three-amino-acid peptide first isolated from human blood that binds copper tightly, forming GHK-Cu, also called copper tripeptide-1.[2] AHK-Cu is a lab-made relative that swaps glycine for alanine.[7]

Tanning peptides are something else. Melanotan II is a ring-shaped version of alpha-MSH, the hormone that tells skin to make pigment, designed to be far more potent than the natural hormone.[13][12] It is injected or sprayed into the nose, not applied as a cosmetic.

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How skin peptides work

  • Collagen signaling: in skin cells grown in the lab, GHK-Cu stimulated collagen production starting at extremely low concentrations.[1] Reviews by its discoverer report effects on many genes involved in repair and antioxidant defense, though independent confirmation is limited.[2][5]
  • Hair follicles: AHK-Cu lengthened human hair follicles kept alive in culture and increased growth of the dermal papilla cells at their base.[7]
  • Pigment: Melanotan II switches on the MC1 receptor on pigment cells, which darkens skin. It also acts on other melanocortin receptors, including ones in the brain thought to trigger its spontaneous erections; nausea is a common side effect.[13][12]

What human trials found

The evidence for copper peptides is weaker than their popularity suggests. The best-known face-cream results come from a 2002 conference presentation and unpublished reports rather than peer-reviewed papers.[2] In the one published randomized trial after CO2 laser resurfacing, GHK-Cu cream did not improve redness, wrinkles or skin quality on objective measures; only patient satisfaction was higher.[3] A 2025 review described a striking lack of clinical studies for anti-wrinkle use,[4] and a 2026 review called GHK-Cu promising but unproven.[5]

For hair, a 2026 randomized, double-blind, split-face trial in Thailand found that a 2% GHK-Cu serum increased eyebrow hair count and thickness in 18 adults over 12 weeks.[6] AHK-Cu has never been tested in a published human trial.[7]

Melanotan II’s human data come from three small University of Arizona studies published between 1996 and 2000.[12][26][27] In the first, 2 of 3 men tanned after five low doses, with nausea and spontaneous erections as side effects.[12]

Topical vs injected peptides

Cosmetic peptides in skincare

Under US law, a cosmetic is something applied to the body to cleanse, beautify or alter appearance, and cosmetics do not need FDA approval before sale. A product becomes a drug when it is intended to treat or prevent disease or to affect the structure or function of the body, and FDA gives claims to restore hair growth, change melanin production or regenerate cells as examples that make a product a drug.[8] That is why peptide serums are marketed for the “look” of firmer skin rather than for rebuilding collagen.

Peptide injections

Injectable copper peptides are not cosmetics and are not FDA-approved drugs. There are no published human studies of GHK-Cu injections.[5][9] FDA has said injectable GHK-Cu may cause immune reactions from clumped peptide or impurities,[10] and dermatologists interviewed by NPR advise against injecting it.[9] Copper itself is a concern at high exposures: the adult upper limit from food and supplements, set by the National Academies and listed by NIH, is 10 mg a day, because chronic high intake can damage the liver,[24] and a 2026 review cautions that this oral limit cannot be converted directly into a safe injected dose.[5]

Tanning injections: moles and melanoma

Melanotan II is the clearest example of a skin peptide with documented harms. Dermatologists have reported new moles and darkening of existing moles within 24 hours of a single injection,[15][16] and several melanomas in users,[17][18] including one inside the mouth of a nasal-spray user.[19] A 2017 dermatology review noted that conclusive proof that melanotan causes melanoma is lacking, but urged caution.[14] Many users combine it with sunbeds, themselves a melanoma risk.[18] Lab testing of internet tanning products found impurities, and vials held 4.32 to 8.84 mg instead of the 10 mg claimed.[22]

The only approved drug in this family is afamelanotide (Scenesse), an implant approved by FDA in 2019 to increase pain-free light exposure in adults with a history of phototoxic reactions from erythropoietic protoporphyria (EPP), a rare inherited disorder. It is not approved for cosmetic tanning.[20]

Who should be most cautious

People with Wilson’s disease, an inherited disorder in which copper builds up in the body, have a high risk of copper toxicity,[24] so extra copper from injected peptides is a particular concern. Anyone who has used a tanning peptide and notices a new mole, or a mole that changes in size, shape or color, should have it checked promptly by a doctor or dermatologist.[25] Copper peptide serums can also be listed on labels as copper tripeptide-1, so check ingredient lists if you are trying to avoid them.

Safety, legality and sports rules

  • GHK-Cu: legal as a cosmetic ingredient but not an approved drug. FDA had placed injectable GHK-Cu on its list of bulk substances that may present significant safety risks in compounding; in April 2026, after the nominations were withdrawn, FDA removed it; it is still evaluating non-injectable GHK-Cu for compounding.[10][11]
  • AHK-Cu: sold as a cosmetic ingredient and not on FDA’s 503A nomination list. Products claiming to regrow hair are regulated as drugs.[11][8]
  • Melanotan II: not approved in any country. In the UK, injectable melanotan is classed as a medicine and cannot legally be sold.[14][21]
  • Sport: none of the three is named on WADA’s 2026 list, but S0 bans any substance without government approval for human use, which covers Melanotan II, at all times.[23]
  • Product quality: injectable and “research use” products are not made to pharmaceutical standards, so content and purity can vary.[22][10]

GHK-Cu also appears among healing peptides and longevity peptides, and Melanotan II among sexual health peptides.