A peptide is two or more amino acids joined together and is the building block of protein. Peptides fall into three main categories: signal peptides, carrier peptides, and those that inhibit nerve signals. Signal peptides, like palmitoyl tripeptide-1, act as messengers to cells, which trigger collagen synthesis, which then increases skin firmness.Palmitoyl tripeptide-1 is a small three amino acid signal peptide with the amino sequence of glycine-histidine-lysine (GHK). GHK is attached to palmitic acid (a fatty acid) to increase its skin penetration and oil solubility.