Topical and Transdermal Peptide Delivery Claims

Topical vs transdermal

• Topical products are meant to act on or in the skin (a cosmetic serum, for example).
• Transdermal products are meant to carry a drug through the skin into the bloodstream.

Cosmetic peptides are covered in skin and cosmetic peptides and peptides in topical formulations.

Why the skin is a hard barrier

A review of protein delivery says proteins are large and water-loving, so they cannot permeate passively across the skin's outer layer (the stratum corneum), which lets through only small fat-loving molecules. [1] A review of peptide delivery says transdermal delivery remains limited by this barrier, and delivery of therapeutic proteins and peptides is still almost entirely by hypodermic needle. [2] Label: established.

A cosmeceutical review lists the same drawbacks: clinical evidence for efficacy is often weak, absorption may be poor because of low fat-solubility, high molecular weight and binding to other ingredients, and prices can be high. [3]

A worked example: acetyl hexapeptide-8

A 2025 review of this ingredient (nicknamed "botox-like") says it has limited permeability through the skin because it is water-loving and relatively large, that whether it reaches neuromuscular junctions remains uncertain, and that its mechanism when applied to skin is incompletely understood. It adds that studies suggest it may reduce wrinkle depth and improve elasticity and hydration. [4] Label: mixed, with small-effect cosmetic outcomes. See acetyl hexapeptide-8. The claim "works like an injection" is a marketing claim unless supported.

Technologies that try to get past the barrier

Reviews list chemical enhancers, conjugation to make a peptide more fat-loving, iontophoresis, electroporation, sonophoresis, microneedles and jet injectors. [2] [1] Several of these disrupt the skin barrier or reach below it, and the protein-delivery review discusses sterility requirements for them. [1] Such methods are research or device-based approaches and are not the same as a cosmetic cream. A claim that an ordinary lotion uses them needs evidence.

Questions to ask about a topical or transdermal peptide claim

1. Which exact ingredient (INCI name) is it, and is the molecule the same as in the cited study? Related: what are cosmetic peptides.
2. Was penetration measured in human skin, or only in a dish or in animals?
3. Is the outcome visible and clinical (such as wrinkle depth) or only a lab marker?
4. Is the delivery technology a device used by a clinician?
5. Does the evidence come from the maker?

For more, use how to evaluate peptide claims and clinic marketing.