Peptides in Skincare: What They Are and What the Research Shows

Peptides are in almost every serum on the shelf now. This is a plain account of what they are, the delivery problem that limits what any of them can do, and what the published research actually found — including where it is weaker than the marketing suggests.

A peptide is a short chain of amino acids — the same building blocks that make up proteins, just far fewer of them. Collagen is a protein of roughly a thousand amino acids; a cosmetic peptide is usually between three and eight. That size difference is the whole story of why peptides ended up in skincare, and it is also the source of most of the confusion about them.

The appeal is straightforward. Many of the short peptide sequences used in cosmetics are fragments that the body itself uses as signals. The idea is that applying such a fragment to skin may prompt a response from the cells that recognise it. That is a reasonable premise, and there is real laboratory research behind several of them. It is also where the honest account has to slow down, because between the premise and the result sits a problem that no amount of marketing copy removes.

The delivery problem, stated plainly

Skin is very good at its job, and its job is keeping things out. The outermost layer, the stratum corneum, is a barrier that excludes most of what is put on it. The most widely cited rule of thumb in this area comes from a 2000 paper in Experimental Dermatology by Bos and Meinardi, which argued that a compound generally needs a molecular weight under about 500 Daltons to cross the intact barrier at all. The authors supported it with three observations: essentially all common contact allergens fall under 500 Daltons, the standard topical drugs used in dermatology are all under 500 Daltons, and so is every compound used in transdermal delivery patches.

Many cosmetic peptides sit near or above that threshold, and they are also water-loving molecules trying to cross a lipid barrier, which compounds the difficulty. This does not mean peptides do nothing. It does mean that any claim resting on a peptide reaching the living layers of skin in a meaningful quantity is a claim about the formulation and the delivery system, not about the peptide alone. Two products naming the same peptide on the label can behave completely differently.

This is the single most useful thing to understand when reading a peptide product page, including ours. The named ingredient tells you what was intended. It does not by itself tell you what arrives.

The families you will actually encounter

Cosmetic peptides are usually sorted into loose functional groups. The boundaries are fuzzy and some peptides sit in more than one, but the grouping is a useful way to read an ingredients list.

Copper peptides

These are peptides bound to copper. The best known is GHK-Cu, or copper tripeptide-1, a naturally occurring copper-binding tripeptide found in human plasma and one of the most-studied peptides in the cosmetic literature — the 2018 review by Pickart and Margolina in the International Journal of Molecular Sciences is the usual starting point. We have written about the GHK-Cu evidence separately and in more detail.

Worth knowing: not every copper peptide on a label is GHK-Cu. Our own Peptide Moisturizer is formulated with Copper Lysinate/Prolinate, which is copper bound to the amino acids lysine and proline — a copper-peptide complex, but a different molecule from GHK-Cu, with its own separate research base. Labels are frequently loose about this distinction and it is worth checking the INCI rather than the marketing name.

Collagen-mimicking and signal peptides

These are fragments designed to resemble sequences found in the skin matrix itself. Tripeptide-29, for example, is a synthetic tripeptide of glycine, proline and hydroxyproline — the repeating motif that makes up much of the collagen molecule. Hexapeptide-11 is another synthetic sequence used in this role. The reasoning is that a recognisable fragment may act as a signal, and this is an active research area rather than a settled one.

Acetylated peptides used for expression lines

Acetyl Hexapeptide-8 is the most-discussed peptide in cosmetic science, and it is worth being precise about what was actually shown. The 2002 study in the International Journal of Cosmetic Science by Blanes-Mira and colleagues tested an oil-in-water emulsion containing ten per cent of the hexapeptide preparation on healthy volunteers, and reported a reduction in wrinkle depth of up to thirty per cent by skin topography analysis after thirty days.

Two caveats belong with that number every time it is quoted. It describes a ten per cent inclusion of the peptide preparation in the test emulsion — higher than the level used in most finished cosmetic products, and note that suppliers generally provide these peptides as dilute solutions, so the figure is not the same thing as ten per cent pure peptide. And it is a single study on a small group. It is genuine published evidence and worth knowing about; it is not a promise attached to any finished product that lists the ingredient. Acetyl Octapeptide-3 is a related synthetic peptide used in the same role.

Eye-contour peptides

Some peptides were developed specifically for the thinner skin around the eye. Acetyl Tetrapeptide-5, used in our Peptide Eye Gel-Cream, is a synthetic four-amino-acid peptide developed by Lipotec for eye-contour formulations. Formulating for this area is as much about texture and tolerability as about the active itself.

Recombinant growth-factor peptides

A newer group, listed on INCI as sh-Polypeptides and sh-Oligopeptides — the "sh-" prefix meaning synthesised and non-animal-derived. These are laboratory-made analogues of human signalling proteins. The research here is mostly laboratory and animal work rather than large human trials, and we have covered that evidence base separately in our article on topical peptides and hair.

How to read a peptide ingredients list

A few practical habits will tell you more than any product description.

Look at where the peptide sits in the INCI list. Ingredients are ordered by concentration down to one per cent, after which order is arbitrary. A peptide near the end of a long list is present in a small amount — which may be entirely appropriate, since several of these are active at low concentrations, but it is information the front of the bottle will not give you.

Check which peptide it actually is. "Peptide complex" and "peptide blend" are marketing terms, not ingredients. The INCI name is the one that can be looked up against published research.

Treat percentage claims carefully. A study run at ten per cent tells you little about a product formulated at a fraction of that, and most brands, ours included, do not publish exact concentrations.

Be sceptical of any topical product described in the language of injectables. Injected treatments and applied-to-skin cosmetics are different categories, regulated differently, and a cosmetic borrowing the vocabulary of a medical procedure is telling you about its marketing rather than its formulation.

What to reasonably expect

Peptides are a well-evidenced area of cosmetic ingredient science with a real delivery constraint sitting on top of it. Used in a well-made formulation, the peptides with published human data behind them are associated with hydration, improved skin texture and improvement in the appearance of fine lines. They work slowly — the published studies that show anything generally run for a month or longer — and they are one part of a routine rather than a replacement for one.

Our topical range — currently pre-launch, with a waiting list rather than a checkout — is formulated around named peptides, with the full INCI published on every product page and the specific peptide identified rather than hidden behind a blend name. These are cosmetic products for external use. Where one of our products contains a peptide discussed here, the INCI on that product page says so. We think the useful thing is to show you which molecule is in the bottle and what the research on it actually found, including where that research is thinner than the category likes to suggest, and let you judge it.

References

Wiley — Bos & Meinardi (2000), The 500 Dalton rule for skin penetration, Experimental Dermatology 9:165-169
Wiley — Blanes-Mira et al. (2002), A synthetic hexapeptide with antiwrinkle activity, Int J Cosmet Sci 24(5):303-310
PubMed — Pickart & Margolina (2018), GHK-Cu regenerative actions

Cosmetic product for external application to the skin. Not a medicine; no therapeutic claims are made. Not for ingestion, inhalation or injection. Patch test before first use.