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Proteins & peptides

Peptides (signal and wrinkle-relaxing)

Also listed as palmitoyl tripeptide-1, palmitoyl tetrapeptide-7, palmitoyl pentapeptide-4, acetyl hexapeptide-8, pentapeptide-18, copper tripeptide-1

Short amino-acid chains meant to signal skin to make collagen or to relax expression lines. Small, mostly manufacturer-run trials; effects are modest.

Limited evidence

What it is

Cosmetic peptides are short protein fragments, often with a fatty acid (palmitoyl) attached to help them into skin. Signal peptides (palmitoyl pentapeptide-4, palmitoyl tripeptide-1, palmitoyl tetrapeptide-7) mimic collagen fragments and prompt fibroblasts to make more matrix in lab tests. Neurotransmitter-inhibiting peptides (acetyl hexapeptide-8, pentapeptide-18) interfere with the nerve signal that contracts facial muscles — in a lab dish — and are sold as a topical alternative to wrinkle-relaxing injections. Copper tripeptide-1 carries copper and is linked to wound healing.

Most are near or above the roughly 500-dalton size that passes easily through skin, which limits how much reaches its target, and they are used at tiny concentrations.

How strong is the evidence?

Limited evidence

Controlled trials are few, small and usually run by ingredient or product makers: a 12-week split-face trial in 93 women found 3 ppm palmitoyl pentapeptide-4 reduced fine lines versus the same moisturizer without it. Trials of the wrinkle-relaxing peptides are small, and none shows effects comparable to injections. Independent replication is scarce.

What it's used for, checked

Fine lines and wrinkles

Mixed

Small improvements in a few controlled, mostly industry-run trials.

Works like wrinkle-relaxing injections

Unproven

A few small trials report shallower wrinkles, but nothing shows these peptides relax muscles the way injections do, and they penetrate skin poorly.

Boosting collagen

Mixed

Shown in lab tests; evidence in people is indirect.

Healing and firming (copper peptides)

Unproven

Mostly lab and wound-healing research.

Works well with

  • Retinoids, vitamin C and sunscreen — peptides are an add-on, not a replacement

Don't combine with

  • Copper peptides and L-ascorbic acid in the same step — copper speeds vitamin C breakdown

Who should be careful

  • Generally well tolerated.
  • Price and the number of peptides in a product aren't a guide to its effect.

The studies

Every citation is checked against its PubMed record.

  1. Topical palmitoyl pentapeptide provides improvement in photoaged human facial skin.
    Robinson LR, Fitzgerald NC, Doughty DG, Dawes NC, Berge CA, Bissett DL · International Journal of Cosmetic Science · 2005 · RCT (split-face)

    93 women aged 35-55 used a moisturizer with 3 ppm palmitoyl pentapeptide on one side of the face and the same moisturizer without it on the other for 12 weeks; the peptide side showed significantly fewer wrinkles and fine lines. Run by a skincare manufacturer.

  2. Role of topical peptides in preventing or treating aged skin.
    Gorouhi F, Maibach HI · International Journal of Cosmetic Science · 2009 · Systematic review

    Reviews controlled ex vivo and in vivo studies of topical peptides and proteins for skin aging, grouping them as signal, enzyme-inhibitor, neurotransmitter-inhibitor and carrier peptides.

  3. The 500 Dalton rule for the skin penetration of chemical compounds and drugs.
    Bos JD, Meinardi MM · Experimental Dermatology · 2000 · Review

    Argues that a compound must weigh under about 500 daltons to pass through the skin's outer layer, based on the size of known contact allergens and of the drugs that work topically or through transdermal patches.