What peptides actually do in your moisturizer (and don't)

A 2024 video on Lab Muffin Beauty Science, where Michelle Wong (a cosmetic chemist with a PhD from the University of Sydney) ran her readers through a bracket-style ranking of skincare actives, put peptides squarely outside her top tier. Retinoids, niacinamide, alpha hydroxy acids, vitamin C, and sunscreen all ranked above. Peptides came in below them, with the caveat that the category is not one ingredient but four loosely related classes, and that the evidence varies by class.

That is the right starting frame. Peptides are not a single thing. The word covers any short chain of amino acids (typically 2 to 50 residues) used in skincare, and four functional categories live under the umbrella. Some have decent evidence. Some have almost none. The ones in your moisturizer probably belong to the category with almost none.

The four jobs peptides are sold to do

Signal peptides tell fibroblast cells to make more collagen. The most common ones in cosmetics are palmitoyl pentapeptide-4 (Matrixyl, the trade name from Sederma) and its cousin palmitoyl tripeptide-1. The mechanism is real: at sufficient concentration, these peptides bind to receptors on the fibroblast and trigger pro-collagen synthesis. The catch is “sufficient concentration.” Most drugstore products dose Matrixyl at fractions of a percent. The Olay Regenerist line, which made Matrixyl famous, gets results in clinical studies but takes 12 weeks to show measurable change in wrinkle depth.

Carrier peptides deliver trace minerals to skin. Copper tripeptide-1 (also called GHK-Cu) is the most studied; it carries copper ions that act as cofactors in enzymes that build the dermal matrix. The Niod Copper Amino Isolate Serum and The Ordinary Buffet + Copper Peptides 1% are the products that take this category seriously; both are pricier than the standard peptide moisturizer because copper-stabilising the formula is harder than just dropping in a peptide powder.

Neurotransmitter-inhibiting peptides are the “Botox in a bottle” class. Acetyl hexapeptide-8 (Argireline) is the marketed one; it interferes with the SNAP-25 protein that lets nerves trigger muscle contractions. Lab Muffin’s coverage notes that at typical concentrations (5 to 10%) it produces about 10 to 15% of the wrinkle reduction a Botox injection delivers, which is real but small. The Ordinary Argireline Solution 10% is the honest dosing. Most “Botox cream” products are not.

Enzyme-inhibiting peptides slow down enzymes that degrade collagen, particularly matrix metalloproteinases (MMPs). The category is the least studied; soybean peptide and rice peptide products claim this mechanism, but the clinical data is thin.

What that means for buying

A few products dose peptides at concentrations that match the published research. The Ordinary Buffet at $12 stacks Matrixyl, Argireline, and copper peptides in one bottle. COSRX The 6 Peptide Skin Booster Serum at $25 dosesa six-peptide cocktail at concentrations the brand publishes in their formulation guide, which alone separates it from competitors that hide behind “proprietary blend.” Medik8 Liquid Peptides Advanced MP at $79 is the high-end choice; it pairs Matrixyl 3000 with neurotransmitter peptides at clinical-trial doses.

Most peptide moisturizers are not in this category. If a $40 cream lists “peptide complex” at the bottom of the ingredient list, behind glycerin, butylene glycol, and silicones, the peptide is doing very little of the heavy lifting. The cream is moisturizing because of the glycerin and the silicones. The peptide name is doing marketing work.

Why they layer well under makeup

Peptides have one underrated practical advantage. They are pH-neutral, fragrance-light, and absorb thinly. Unlike vitamin C, they do not pill under foundation. Unlike retinol, they do not flake. Unlike AHAs, they do not loosen the dead-cell layer that primer needs to grip onto.

That is why they show up in pre-event routines. A model going into a clean girl tutorial shoot at 7am will often have a thin layer of The Ordinary Buffet under their tinted moisturizer; the peptides give the skin a slightly plumped finish, and the formula does not interfere with the makeup pickup. The same logic applies to a no-makeup makeup look, where the foundation coverage is so light that any base instability shows immediately. Peptide serum is one of the safest bets you can put on first.

For a glass skin finish, peptides do less work than the humectants and the occlusive layer above them, but they do not fight the look. The plumping signal peptides give over time can make the glass effect more convincing because the skin underneath is fractionally fuller.

What peptides will not do

They will not replace retinoids. The published gap in wrinkle reduction between a stable 0.5% retinol and a top-tier peptide stack is roughly 3 to 1 over a six-month trial. Wong has been explicit about this in her bracket coverage: if you have to pick one anti-ageing ingredient, retinoids are the correct answer.

They will not act as Botox. Argireline produces measurable softening of expression lines, but the effect is partial and reversible the moment you stop using it. A neuromodulator injection lasts three months. A serum effect lasts the duration of the active substance on the skin, which is hours.

They will not penetrate to the dermis at meaningful concentration without help. The skin barrier is built to keep large molecules out. Peptides over a few hundred Daltons in molecular weight have to be either tiny (Argireline is small) or carried by a delivery system (some products use liposomes or palmitoyl tags) to reach the layers where they could matter.

A reasonable place to put them

Use a peptide serum if you have already locked in the basics: daily SPF, a retinoid two or three nights a week, and a vitamin C in the morning. Layer the peptide serum after vitamin C and before moisturizer. Use it twice a day. Expect quiet, slow returns over a quarter, not dramatic transformations.

If you are skipping any of the basics to make room for peptides, you have the priority order wrong.

The bigger picture, if you are reading slaye for the why behind a routine, is that peptide marketing has run ahead of peptide science by roughly a decade. The molecules are real. The clinical effects are modest. Anyone who tells you their cream is “Botox in a bottle” is either selling Argireline at a polite dose or selling you nothing at all.