What are peptides? Collagen, creams, medicines, research

Peptides are short chains of amino acids. Amino acids are the building blocks of proteins. In a peptide they are joined one after another by a chemical bond called a peptide (amide) bond. The order of the amino acids in the chain is called the sequence, and it determines which peptide each one is.

The word "peptides" is heard today in very different settings: in collagen supplements, in face creams, in medicines and in laboratories. This guide explains what a peptide is as a molecule, which peptides the human body itself makes and how the four kinds of products that share the same name differ. Where published studies in humans exist, they are cited with their source.

A peptide and a protein are made of the same amino acids, joined by the same bond. The difference is mainly size. By convention, chains of more than about 50 amino acids are usually called proteins. This boundary is not strict: IUPAC, the international body that sets chemical terminology, notes that authors differ greatly on where the term begins.

Depending on length, more specific terms are also used. A dipeptide has two amino acids and a tripeptide three. Very short chains are called oligopeptides and longer ones polypeptides. For example, GHK, described below, is a tripeptide, while oxytocin has 9 amino acids. So when someone says "a peptide", they mean one specific molecule with a specific sequence, not a general category of products.

The human body makes many peptides that act as chemical messengers. Peptide hormones are synthesised from amino acids and act throughout the body, while neuropeptides are released by nerve cells.

Two well-known examples:

• Oxytocin is a hormone of 9 amino acids.
• Insulin is a pancreatic hormone of 51 amino acids in two chains. With 51 amino acids it sits right on the conventional boundary between peptide and protein.

The first chemical synthesis of a polypeptide hormone in the laboratory was recognised with the 1955 Nobel Prize in Chemistry. The synthesis showed that a peptide with a known sequence can be made chemically, which later became a basic tool of biochemical research.

In everyday language the word "peptides" is used for products that have nothing to do with each other: food supplements, cosmetics, medicines and laboratory research materials. They belong to different categories and are governed by different rules.

This matters in practice for anyone reading about peptides: a result measured for one of them does not carry over to the others, even if they are all called "peptides". At a glance:

• Collagen peptides: a mixture of collagen fragments, sold as a food supplement and regulated as foods.
• Peptides in cosmetics: synthetic ingredients in creams and serums, regulated as cosmetics.
• Peptide medicines: specific molecules with a marketing authorisation, usually on prescription.
• Research peptides: synthetic materials for laboratory research, which have not been approved as medicines and are not intended for human use.

The following sections look at them one by one.

"Collagen peptides", also called "hydrolysed collagen", are collagen broken down into smaller pieces. Collagen is a protein, and the collagen used in products usually comes from animal bones, skin and tendons. Collagen peptides are sold mainly as food supplements. They are not one specific molecule but a mixture of many small collagen fragments.

What has been measured in humans:

• In healthy volunteers, after consumption of gelatin hydrolysates, small collagen-derived peptides were detected in the blood. The main one was the dipeptide prolyl-hydroxyproline (Pro-Hyp) (Iwai et al., J Agric Food Chem 2005, PMID 16076145).
• In a randomised, double-blind, placebo-controlled study, 69 women aged 35 to 55 were divided into two hydrolysed-collagen groups and one placebo group, for 8 weeks. Skin elasticity, the primary interest of the study, was measured statistically significantly higher in both collagen groups compared with placebo. In the older women, elasticity was measured statistically significantly higher also 4 weeks after the end of the study. For skin moisture the difference did not reach statistical significance (Proksch et al., Skin Pharmacol Physiol 2014, PMID 23949208).

In the European Union food supplements are foods (Directive 2002/46/EC). Health claims for foods are allowed only when they are included in the Union list under Regulation 1924/2006.

The data in this section concern collagen peptide supplements, which are foods, and not research peptides, which are not intended for human use.

A randomised, double-blind, placebo-controlled study was completed by 53 men with a mean age of 72 years and sarcopenia, that is, reduced muscle mass and strength due to age (Zdzieblik et al., Br J Nutr 2015, PMID 26353786). All followed a guided resistance-training programme for 12 weeks, together with collagen peptides or with a placebo.

After the programme, body composition and muscle strength had changed statistically significantly in both groups compared with the start. In the collagen peptide group the changes were larger (P < 0.05).

The study concerned one specific group of older men, together with an exercise programme, and does not generalise to other groups of people. It is not evidence about the research peptides Avenor supplies, nor about their use by people. According to a correction published in 2025 (PMID 40859798), a collagen manufacturer supplied the study samples and covered the costs of participant compensation and sample analysis, and one of the authors is named as a co-inventor of a patent application relating to the active substance studied.

In serums, creams and shampoos, "peptides" are cosmetic ingredients, usually small synthetic peptides. A 2025 review groups them, by mechanism of action, into four families: signal peptides, carrier peptides, neurotransmitter-inhibitor peptides and enzyme-inhibitor peptides. The same review notes as a main limitation the poor permeability of peptides through membranes, which limits their delivery to the site where their action is studied (Pintea et al., Biomolecules 2025, PMID 39858482).

In humans, in a 12-week randomised study of 93 women aged 35 to 55, each participant had a moisturiser containing the peptide palmitoyl pentapeptide (pal-KTTKS) on one side of the face and the same moisturiser without the peptide on the other. Image analysis measured a statistically significant difference in favour of the peptide side for wrinkles and fine lines (Robinson et al., Int J Cosmet Sci 2005, PMID 18492182). The authors came from a cosmetics company.

In the European Union cosmetics are governed by Regulation 1223/2009, which defines them as products for the external parts of the body intended for cleaning, protecting or changing appearance.

The "copper peptide" is usually GHK-Cu: a tripeptide of three amino acids, glycine, histidine and lysine, that binds copper ions. Its sequence was identified in 1977 as a blood serum tripeptide (Schlesinger, Pickart and Thaler, Experientia 1977, PMID 858356). It is sold as a cosmetic ingredient under the name "copper peptide".

Despite the similar name, it is not the same as collagen peptides: GHK-Cu is one specific molecule with copper, while collagen peptides are a mixture of collagen fragments. What was measured in the studies and what we do not know is in the article GHK-Cu, the copper peptide: what it is and what the studies show.

Some peptides are sold as medicines with a marketing authorisation and are usually available on prescription. The best-known historical example is insulin: its clinical use began in 1922 and its discovery was recognised with the 1923 Nobel Prize in Medicine.

According to a 2021 review, early efforts in the field focused on human hormones, and design techniques and peptides derived from other organisms were added later. Reviews of the literature record dozens of peptide medicines on the market worldwide, in very different medical fields (Muttenthaler et al., Nat Rev Drug Discov 2021, PMID 33536635; Wang et al., Signal Transduct Target Ther 2022, PMID 35165272). Each such medicine goes through clinical trials and assessment by a medicines authority before it receives a marketing authorisation. This process does not apply to supplements, cosmetics or research peptides.

Research peptides are synthetic materials intended for laboratory research, for example in studies of cell signalling, tissue biology or cellular metabolism. The Research Use Only (RUO) label states their intended purpose: they have not been approved as medicines and are not intended for human or veterinary use.

The RUO label is not a quality certification; it only describes the intended purpose of the material. The quality of a specific batch is documented separately, with analyses such as those described below.

In other words, they are not the medicines of the previous section, nor supplements or cosmetics. Data from human studies on a medicine, a supplement or a cosmetic do not carry over to a research material, even if the names are similar.

In the European Union, and therefore in Greece, medicines for human use are subject to authorisation rules before they are placed on the market (Directive 2001/83/EC). The "RUO" label is not an authorisation for use in humans. The regulatory classification of a product depends on its characteristics, its presentation and its intended use.

Avenor materials are research materials for laboratory use. They are not intended for human or veterinary use, or for the diagnosis or prevention of disease, and no usage instructions are provided. For any health matter, the right person to ask is a healthcare professional. More on the framework in the article Peptides and safety: what applies in Greece.

A widely used method for making synthetic peptides is solid-phase synthesis: the chain is built on a solid support, one amino acid at a time, through repeated chemical steps. Bruce Merrifield published the method in 1963 and received the 1984 Nobel Prize in Chemistry for it (Merrifield, Biosci Rep 1985, PMID 4027355, the prize lecture). According to a 2022 review, peptides for pharmaceutical use are produced and modified by both chemical and biological methods (Wang et al., Signal Transduct Target Ther 2022, PMID 35165272). At the end of production, peptides are usually lyophilised (dried by sublimation) and supplied as a powder.

Two key analytical methods are high-performance liquid chromatography (HPLC), used for purity, and mass spectrometry (MS), which confirms the molecular mass and so helps confirm the identity of the peptide. The results are recorded in a Certificate of Analysis (COA), together with the laboratory that ran the analysis and the batch number it refers to. At Avenor, a COA is published where available in the COA library; coverage is not yet complete for every batch.

A COA is of value when its batch number matches the specific material and when the laboratory, the date and the method of the analysis are stated.

• The three randomised studies presented here had 53 to 93 participants and lasted 8 to 12 weeks, and several have authors from companies or institutes in the sector.
• Each study concerns a specific product, a specific composition and a specific group of people. Its result does not carry over to other products that are also called "peptides".
• In the study in older men with sarcopenia, the comparison was with a placebo containing no protein (silica), and the study had financial and patent links to the collagen sector. It therefore does not show whether the difference concerns collagen specifically or protein intake in general.
• For peptides in cosmetics, the literature itself reports poor permeability through membranes, so it is not always clear how much of the substance reaches the site being studied.
• For research peptides, the data come mainly from laboratory studies. Research in humans, where it exists, is at an early stage.
• Terminology has no strict boundary between peptide and protein, so the same term is used with a different scope by different authors.

• Iwai K et al. J Agric Food Chem. 2005. PMID 16076145 · DOI 10.1021/jf050206p
• Proksch E et al. Skin Pharmacol Physiol. 2014. PMID 23949208 · DOI 10.1159/000351376
• Zdzieblik D et al. Br J Nutr. 2015. PMID 26353786 · DOI 10.1017/S0007114515002810 · Correction 2025: PMID 40859798 · DOI 10.1017/S000711452510425X
• Robinson LR et al. Int J Cosmet Sci. 2005. PMID 18492182 · DOI 10.1111/j.1467-2494.2005.00261.x
• Pintea A et al. Biomolecules. 2025. PMID 39858482 · DOI 10.3390/biom15010088
• Schlesinger DH, Pickart L, Thaler MM. Experientia. 1977. PMID 858356 · DOI 10.1007/BF02002806
• Muttenthaler M et al. Nat Rev Drug Discov. 2021. PMID 33536635 · DOI 10.1038/s41573-020-00135-8
• Wang L et al. Signal Transduct Target Ther. 2022. PMID 35165272 · DOI 10.1038/s41392-022-00904-4
• Merrifield B. Biosci Rep. 1985. PMID 4027355 · DOI 10.1007/BF01116553
• Merrifield RB. J Am Chem Soc. 1963. DOI 10.1021/ja00897a025
• IUPAC-IUB JCBN. Nomenclature of amino acids and peptides, rule 3AA-11.
• IUPAC. Glossary of class names of organic compounds. 1995 (steroids).
• U.S. National Library of Medicine. MeSH: Peptides, Peptide Hormones, Neuropeptides, Oxytocin, Insulin, Steroids.
• Directive 2001/83/EC (medicinal products for human use) · Directive 2002/46/EC (food supplements) · Regulation (EC) 1924/2006 (health claims) · Regulation (EC) 1223/2009 (cosmetics).
• Nobel Foundation: Medicine 1923, Chemistry 1955, Chemistry 1984.

An informational text summarising published research. It is not medical advice or usage guidance.