Peptides in skin care: Palmitoyl Pentapeptide-4, Acetyl Hexapeptide-8, Copper Tripeptide-1 and more
Peptides have some of the longest names on an INCI list. What “palmitoyl”, “tripeptide” and the number at the end mean, which peptide groups are common in skin care, and why the amount in a jar is usually tiny.
Updated: 31 October 2026 · Reviewed by: Kamil Pyziak
What peptides are
Peptides are short chains of amino acids, the same building blocks that make up proteins. In skin care the word usually refers to specific, laboratory-made sequences of two to about ten amino acids, designed to resemble fragments of natural proteins or messenger molecules.
They are popular in “anti-ageing” serums and eye creams. Most are made by chemical synthesis, which allows the supplier to control the exact sequence; the INCI name then describes that structure in a standardised way.
How to decode a peptide INCI name
Take Palmitoyl Tripeptide-1. The first part, Palmitoyl, Myristoyl or Acetyl, names a group attached to the chain: palmitoyl and myristoyl are fatty-acid residues that make the peptide more oil-friendly, acetyl is a small group often used to make it more stable. The middle part tells you the number of amino acids: di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6) and so on.
The final number is just a serial number in the INCI naming system that distinguishes different peptides of the same length. Palmitoyl Tripeptide-1 and Palmitoyl Tripeptide-5 are two different molecules; the higher number does not mean stronger or newer in any meaningful sense. Names can also change: Acetyl Hexapeptide-8 was previously listed as Acetyl Hexapeptide-3.
Common peptide groups
Suppliers and textbooks often sort cosmetic peptides by their intended role. So-called signal peptides, such as Palmitoyl Pentapeptide-4, Palmitoyl Tripeptide-1 and Palmitoyl Tripeptide-5, are designed to resemble fragments of skin proteins such as collagen. Palmitoyl Tetrapeptide-7 is often paired with Palmitoyl Tripeptide-1 in a well-known commercial blend.
Acetyl Hexapeptide-8 is described as a “neurotransmitter-affecting” peptide and is marketed for expression lines; it is not comparable with injectable treatments. Copper Tripeptide-1 is a carrier peptide that binds copper and gives some products a blue tint. In lash and brow serums you may find Myristoyl Pentapeptide-17. These labels describe the concept behind the ingredient, not a proven effect in any particular product.
How strong is the evidence?
Peptides are interesting ingredients, but much of the published data comes from raw-material suppliers, often from laboratory studies or small trials with their own formulas. Independent, larger studies are less common. Whether a peptide reaches its target in the skin depends on its size, its attached groups and the whole formula.
Peptides are also not the same as hydrolysed proteins. Hydrolyzed Collagen or Hydrolyzed Wheat Protein are mixtures of protein fragments of various sizes; they mainly form a film and help skin and hair hold moisture, and they are not designed as specific signal molecules.
How much peptide is in a product?
Peptides are expensive and are effective, according to suppliers, at very low levels. They are usually delivered as dilute solutions in water, glycerin, butylene glycol or similar solvents, often with their own preservatives. That is why peptides often appear near the end of an INCI list, sometimes surrounded by the solvents they came with.
A claim such as “10% peptide complex” usually refers to the amount of that ready-made solution, not to the pure peptide. This is normal practice, but it means headline percentages say little about the real peptide content.
Practical notes
Peptides are generally considered gentle and are often combined with humectants, niacinamide or other actives. Some brands advise using copper peptides separately from strong exfoliating acids or pure vitamin C; follow the product’s own instructions.
Peptide serums are cosmetics. Questions about skin changes, persistent irritation or medical procedures are best discussed with a doctor.
What the label does not tell you
The INCI list names the peptides but does not show their concentration, the amount of solution they came in or the evidence behind them. Several peptides listed together may look impressive while each is present in a trace amount.
Peptide names are precise but not self-explanatory. Use the name to look the ingredient up, and treat marketing nicknames and comparisons with medical treatments with caution.