A review published in 2024 in the Journal of Cosmetic Dermatology gathered the last decade of peptide penetration research. The headline is not revolutionary. It is clarifying.
Peptides have poor oral bioavailability and, when applied topically, poor skin penetration. The stratum corneum is a brick-and-mortar barrier of corneocytes and lipids. Most peptides sit on top or penetrate only the uppermost layers. Cosmetic chemists have spent years trying to solve this.
What works
The review identifies several strategies with evidence behind them. Chemical conjugation—attaching a fatty acid like palmitic acid—improves lipid affinity and helps peptides slip between corneocytes. Liposomes, niosomes, and solid lipid nanoparticles encapsulate peptides and protect them from degradation. Microneedling creates physical channels that bypass the stratum corneum entirely, though that moves the procedure out of daily skincare.
Penetration enhancers such as ethanol, propylene glycol, and certain terpenes can disrupt lipid packing temporarily. The review notes that these come with irritation trade-offs, especially at higher concentrations.
What remains uncertain
Most studies measure peptide delivery to skin layers, not to a specific biological target. A peptide may reach the epidermis without ever reaching a fibroblast in the dermis. Manufacturers often extrapolate from in vitro receptor studies, assuming that if a peptide binds a receptor in a dish, the same happens in intact skin. That leap is not always justified.
The practical angle
The review does not doom topical peptides. It frames them as promising but delivery-dependent. A peptide in a well-formulated base may reach enough depth to matter. A peptide in a basic aqueous serum probably will not.
For consumers, the lesson is to favor specific, named peptides from established suppliers and to be skeptical of formulas that rely on peptide blends with no delivery technology. Penetration is the bottleneck. The best peptides on paper mean nothing if they cannot get in.