A chemical modification that adds a small molecular cap to a peptide, usually to make it more stable or to help it cross into skin cells.An acetyl group is added, typically at the N-terminus of a peptide. Acetylation increases lipophilicity, improves membrane permeability, and extends half-life by blocking degradation at the peptide’s exposed end. Commonly used in cosmetic peptides (e.g., acetyl hexapeptide-3 / argireline) to enhance transdermal penetration.