Some peptides have peer-reviewed evidence; many marketed as anti-aging ingredients do not. The picture is more nuanced than the industry suggests.
Peptides in skincare fall into three functional classes:
Signal peptides. Molecules like palmitoyl pentapeptide-4 (Matrixyl) that mimic collagen breakdown fragments and trigger fibroblast activity. Small clinical studies show modest improvements in fine lines and skin thickness over 3-6 months. Effect size is smaller than retinol.
Carrier peptides. Copper peptide (GHK-Cu) is the best-known. Real evidence for wound healing, anti-inflammatory effects, and collagen and elastin synthesis (Pickart, 2018). Concentration and formulation matter significantly.
Neurotransmitter-inhibiting peptides. Acetyl hexapeptide-8 (Argireline) claims to reduce muscle contraction like a topical Botox. Some evidence for reducing dynamic wrinkles, but effect size is small and dependent on high concentration and prolonged use.
Enzyme-inhibiting peptides. Peptides designed to inhibit MMPs. Emerging evidence, most in vitro rather than in vivo.
Errante's 2020 review provides a systematic overview of the peptide classes and their evidence base (Errante, 2020).
Practical: peptides are worth trying if used at effective concentrations from established formulators. They're modest additions — not replacements — for higher-evidence actives like retinoids and vitamin C.