Matrixyl, or palmitoyl pentapeptide-4, is a five amino acid peptide attached to a fatty acid chain that helps it cross the skin barrier. The peptide portion is a fragment of type I collagen, and the idea is that its presence signals to skin cells that collagen has been damaged, prompting them to produce more. That is a reasonable mechanism and it has some supporting evidence, though much of it comes from the manufacturer and independent controlled trials are scarce. It is a legitimate cosmetic ingredient with a modest, real effect. The perspective worth keeping is that topical retinoids and daily sunscreen have vastly more evidence behind them for the same goal, and cost less.