Peptides are short chains of amino acids — typically 2 to 50 residues — that function as signalling molecules in the skin. They are not structural building blocks themselves (despite the common metaphor of collagen peptides replenishing collagen). Instead, they bind to specific receptors on cell membranes and trigger intracellular pathways that regulate gene expression, protein synthesis, and cellular behaviour.
Different peptides activate different pathways. Signal peptides like GHK-Cu bind to fibroblast receptors and upregulate collagen and elastin gene transcription. Carrier peptides transport trace elements (like copper) across cell membranes. Neurotransmitter-inhibiting peptides (e.g., Argireline / acetyl hexapeptide-8) mimic the action of botulinum protein by preventing SNARE complex formation, thereby reducing muscle contraction that causes expression lines.
The specificity of peptide action is concentration-dependent. At very low concentrations (nanomolar), many peptides have no measurable effect. At moderate concentrations, they support repair pathways. At high concentrations, they can saturate receptors and produce a diminished response. This bell-shaped dose-response curve is one of the most common reasons for peptide formulation failure — too little does nothing, too much is wasteful.
Peptides face two delivery challenges: they are large (typically 500-2000 daltons) and they are water-soluble. Both properties limit stratum corneum penetration. Encapsulation in liposomes or conjugation with fatty acids (palmitoylation) increases bioavailability. A palmitoylated peptide can achieve 5-10× greater skin penetration than its unconjugated form.
The proliferation of peptide ingredients in commercial skincare has created confusion about mechanisms. Most peptide blends on the market combine 3-5 peptides targeting different pathways. The total system effect — whether they synergise or compete for receptor binding — depends on relative concentrations and delivery kinetics, which vary significantly between formulations.