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What signal peptides actually are.
Signal peptides are short sequences (usually 3–6 amino acids) modelled on fragments released during native collagen breakdown. The premise: fibroblasts interpret these fragments as a signal that collagen is being damaged and respond by upregulating new collagen synthesis. Matrixyl (palmitoyl pentapeptide-4) is the most-studied; the rest of the field is a long tail of variations on that biology with weaker independent data.
The honest framing: the biology is reproducible in vitro, the in-vivo cosmetic effect is real but slow, and the gap between marketing claims and clinical results is wider here than for almost any other active. Manage expectations and you will not be disappointed.