Are there any risks associated with the use of peptides?

The peptides are small proteins composed of chains of amino acids linked together by peptide bonds. Some amino acids are termed essential, as the body cannot synthesise them and must obtain them via through diet. The diversity of possible combinations allows for the formation of molecules with a wide range of properties, capable of interacting with specific skin cells and enzymes, as well as with hair follicles.

In cosmetics, peptides are used for their varied biological activities: some can stimulate the production of collagen and elastin, two fibrous proteins that give the dermis its suppleness and elasticity, while others possess anti-inflammatory properties and promote skin healing. Still others, such as those derived from peas, target hair follicles to support the growth of hair, eyelashes and eyebrows. In INCI lists, peptides are recognised by prefixes indicating their length: di-, tri-, tetra- and pentapeptides, and appear in various forms such as tetrapeptide-2, acetyl-tetrapeptide-15, hexapeptide-2 or cyclopeptide-5.

There are no contraindications to the topical use of skincare products containing peptides, and even pregnant and/or lactating women may use them.

Moreover, peptides are often identical or analogous to protein fragments already present in the body, which considerably reduces the risk of side effects. They are generally very well tolerated by all skin types, even the most sensitive, and the risk of allergy is extremely low. The majority of peptides used in cosmetics have been assessed in various clinical studies, and no serious reactions have been reported. Very rarely, isolated cases of redness have been observed, but these remain exceptional.

Several studies detail this safety profile, including one conducted with peptide 14, a peptide developed to modulate cellular senescence in the skin. Fibroblasts and keratinocytes were cultured for 24 hours in the presence of increasing doses of peptide 14 (0.01–100 µM). The results of the MTT cell viability assay showed that the peptide did not affect cell survival, even at the highest concentration of 100 µM. For reference, this assay assesses cell health by measuring the cells’ ability to reduce the tetrazolium salt MTT to formazan, which indicates metabolic activity.

The study also tested peptide 14 on human skin equivalents according to OECD 439 recommendations for reconstructed skin models. The results showed that no concentration of the peptide reduced skin tissue viability. On the contrary, all tested doses slightly improved viability compared with untreated tissues. Qualitative histological analysis confirmed epidermal integrity: the basal layer and epidermal stratification were preserved, with no alteration in epidermal thickness, which is a good indicator of skin tolerance.

Finally, a patch test was carried out on 54 participants aged 18 to 77 years, exposed to 1 mM of peptide 14 on the back under semi-occlusion, for a total of nine alternating applications over three weeks, followed by a final test on an untreated area ten days later. No participant showed any skin reaction, whether irritation, redness, swelling or itching, confirming the safety of peptide 14 even under conditions of repeated application.

However, as with all topical skincare treatments, we still recommend conducting a skin tolerance test before incorporating it into your routine. To do so, apply a small amount of the product to the crease of your elbow and leave it on for 24 hours. If you observe any reaction, do not apply it to the rest of your skin or to your hair.

Note : The diversity of peptides and their structures, however, makes it difficult to generalise their safety profile, as each molecule may behave differently depending on its composition and size.

• LINTNER K. Peptides: What else? Cosmeticobs (2014).

• ALMEIDA I. F. & al. Trending anti-aging peptides. Cosmetics (2020).

• CARVALHO J. L. & al. In vitro and in vivo toxicity assessment of the senotherapeutic Peptide 14. Toxicology Reports (2022).