Not all peptides do the same thing. The cosmetic industry often treats"peptide" as a single ingredient class, but biologists sort them by function. Three categories cover most of what you will see on a label.
Signal peptides
Signal peptides tell cells to perform a task. In skincare, the task is usually making more collagen, elastin, or other matrix components. Palmitoyl pentapeptide-4, the original Matrixyl ingredient, is the classic example. Its sequence is designed to mimic a collagen breakdown product, tricking fibroblasts into ramping up repair.
Signal peptides are the most common type in anti-aging products. They are also the hardest to validate in vivo, because measuring new collagen in living human skin requires biopsy or sophisticated imaging.
Carrier peptides
Carrier peptides shuttle trace elements to cells. GHK-Cu is the best known. It binds copper and delivers it to tissues where copper-dependent enzymes operate. Other carrier peptides exist for manganese and selenium, though they are less common in cosmetics.
The mechanism is straightforward: the peptide itself is a delivery vehicle. The benefit comes from the mineral it carries. That is why copper peptide discussions often overlap with wound healing and tissue repair.
Neurotransmitter peptides
Neurotransmitter peptides aim to reduce muscle contraction. Argireline, or acetyl hexapeptide-8, is the flagship. It interferes with the SNARE complex, the molecular machinery that lets nerve vesicles release acetylcholine. Less acetylcholine means less muscle pull means fewer expression lines.
The effect is weaker than botulinum toxin and depends heavily on penetration. These peptides are popular in eye creams and forehead serums.
Why the categories matter
A product that claims to "boost collagen" using a neurotransmitter peptide is misaligned with the science. A product that claims to "relax wrinkles" using a signal peptide is equally off. Knowing the category lets you match the peptide to the claim.
Most advanced formulas combine categories. A serum might use a signal peptide for collagen, a copper peptide for repair, and a neurotransmitter peptide for expression lines. That is fine. Just do not assume any peptide will do any job.