Pentapeptides are a type of peptide where the peptide has five ("penta") amino acids. There are dozens of pentapeptides used in cosmetic products, with some having more research than others, though most have at least some research from the company that developed and sells the peptide (or peptide blend) to cosmetics companies. Examples of pentapeptides include myristoyl pentapeptide-10 and acetyl pentapeptide-1. Such peptides are theorized to function as cell-communicating ingredients, though this assumes they're formulated in a way that they can actually reach the target areas of cells intact, which is open to debate. Still, pentapeptides likely help boost skin's moisture content and they're not harmful ingredients.
palmitoyl pentapeptide 3