A 5% peptide serum sounds stronger than a 1% peptide serum. Often it is not.
Concentration is one variable among many. Peptide efficacy depends on molecular weight, stability, penetration, formulation pH, and the presence of penetration enhancers. A high concentration of a peptide that cannot cross the skin barrier is mostly expensive water.
Molecular weight matters most
The stratum corneum blocks molecules larger than roughly 500 Daltons. Many peptides are larger. A 1% solution of a tiny, stabilized peptide may reach living skin cells more effectively than a 10% solution of a bulky one.
Manufacturers address this by attaching fatty acid chains—palmitoyl, myristoyl—or by encapsulating peptides in liposomes. These modifications improve penetration. A low concentration of a palmitoylated peptide can outperform a high concentration of the same peptide without the fatty tail.
Stability and pH
Peptides are strings of amino acids held together by peptide bonds. Strong acids, strong bases, and certain enzymes break those bonds. A formula at pH 3.5 might degrade a peptide within weeks. The label percentage reflects what went into the bottle, not what remains on your bathroom shelf six months later.
Purity matters too
Raw peptide quality varies. A cheap peptide may contain truncated fragments, residual solvents, or counterions that do nothing for skin. Reputable suppliers provide certificates of analysis and specify peptide content. Most brands do not publish this information.
How to shop smarter
- Look for the specific peptide name, not just "peptide complex."
- Favor products that disclose the form: palmitoyl, acetyl, or copper-bound.
- Check packaging. Airless pumps and opaque bottles protect fragile peptides.
- Ignore concentration brags unless the brand also explains delivery.
Percentage is a marketing number. Biology is the test.