What Are Peptides

Peptides are short chains of amino acids. When two or more amino acids are joined by a peptide bond, a peptide is formed. Once the chain grows beyond roughly fifty amino acids, we no longer speak of a peptide but of a protein. The boundary is not sharp and different sources place it in different spots, but the principle is simple: a peptide is short, a protein is long.

In the body, peptides do all kinds of jobs. Some are hormones, some take part in carrying signals between cells, and some have a role in the immune response. It is precisely this signalling role that makes peptides interesting to the cosmetics industry.

How peptides are named

The name of a peptide usually tells you how many amino acids it contains. The prefix comes from Greek:

• dipeptide: two amino acids
• tripeptide: three
• tetrapeptide: four
• pentapeptide: five
• oligopeptide: a few, usually up to about ten
• polypeptide: many, already close to a protein

This is why the ingredient list of a cosmetic product will show names such as Acetyl Tetrapeptide-3 or Palmitoyl Tripeptide-1. The number at the end is not a concentration or a strength, it identifies a particular molecule within that group.

The prefix at the start, such as acetyl, palmitoyl or biotinoyl, marks a molecule attached to the peptide to change how it behaves, most often so that it passes more easily through the lipid layer of the skin or stays more stable in the formulation.

Peptides in cosmetics

In cosmetics, peptides are used as so-called signalling ingredients. The idea is that a short chain of amino acids resembles a fragment of some natural protein and that, on contact with a cell, it may take part in the communication that goes on in the skin anyway.

The peptides most often found in cosmetics fall roughly into a few groups:

• signalling peptides: the largest group in skincare products
• carrier peptides: they bind trace elements, the best known example being the copper tripeptide GHK-Cu
• enzyme inhibitors: they slow the breakdown of certain structures in the skin
• neurotransmitter peptides: they affect muscle contraction and are familiar from products aimed at facial expression lines

We covered each group in more detail, along with how to read INCI names, in the article Peptides in cosmetics.

What peptides in cosmetics are, and what they are not

It is worth being precise here, because a fair amount of exaggeration has built up around peptides.

A peptide in a cosmetic product is an ingredient. The research cited for individual peptides has most often been carried out on cell cultures or under limited conditions, with a particular concentration and a particular carrier. The result of such research says something about the ingredient, but it does not automatically say anything about the finished product containing it.

A finished product works or does not work depending on concentration, formulation, how it is applied and, in the case of skin, on how much of the ingredient can get through the surface layer at all. It is therefore reasonable to view a peptide as an ingredient with a reason to be in a formulation, not as a guarantee of an outcome.

Peptides as medicines

There are also peptides that are registered medicines. They are prescribed, dosed and used under medical supervision, and they have little in common with cosmetic peptides beyond the chemical class. A cosmetic product containing peptides is not a substitute for a medicine and should not be treated as one.

Why peptides come up in connection with hair

The skin of the scalp is skin like any other, with its own cycles and its own structure. Peptides used in skincare have found their way into scalp products too, where they are combined with application methods that help spread them evenly.

If you want to know what exactly goes into products of this kind and how they differ, have a look at the article Hair serums and ampoules.

In short

A peptide is a short chain of amino acids. In cosmetics it is used as a signalling ingredient and appears under an INCI name with a prefix and a number. It is worth knowing and worth reading on a label, but it should not be confused with a medicine, nor should it be expected to deliver what a single ingredient cannot deliver on its own.

Related: The range of SORA peptide complexes