Everything you need to know about peptides in cosmetics.

Peptides are small proteins. They are composed of chains of amino acids (aa) linked together via peptide bonds. In nature, there are approximately 500 amino acids; however, only 20 are present in the human body. These can be combined to create a wide variety of molecules, called proteins ( molecular mass greater than 10,000 Daltons or about 100 aa) or peptides (less than 100 aa). Of these 20 amino acids present in the human body, 9 are not naturally synthesised by the body and must be supplied to it through diet: they are called essential amino acids. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The history of peptides in skincare and haircare dates back around fifty years. At that time, these were often of animal origin, derived for example from the hydrolysis of a protein called keratin, taken from bird feathers. This chemical reaction was not very specific, so the peptide fragments obtained varied in size and amino acid combination. Despite this, a plethora of cosmetic products contained these peptides under the I.N.C.I. names "Hydrolyzed Collagen/Elastin/Keratin/Silk...", primarily due to their low costs and hygroscopic properties.

Following the "mad cow" crisis in the early 90s, cosmetic ingredients of animal origin have increasingly been controversial, and 100% synthetic peptides have emerged. However, these took some time to conquer the cosmetic market, even though studies were encouraging regarding the biological activities of certain peptides on the stimulation of collagen synthesis in fibroblasts. This can be explained by the fact that peptides, due to their hydrophilic characteristics, have virtually no chance of penetrating the stratum corneum to reach the dermis if they are added as they are in a formula.

By adding a fatty acid to a peptide chain (this is then referred to as a lipopeptide), researchers have nonetheless managed to ensure its trans-epidermal penetration. The lipopeptide could then fulfil its biological function, namely stimulating collagen synthesis. From the 2000s onwards, these advances in research have propelled peptides as key actives in skin ageing, among other things.

The primary role of exogenous peptides is to effect changes in the complex pathways regulating the expression of skin proteins, generally to prevent signs of ageing. In other words, peptides are most often used to trigger a signalling cascade and stimulate the production of collagen and elastin. These fibrous proteins present in the dermis ensure flexibility and firmness to the skin, but their content in the skin tends to decrease over the years. Moreover, certain peptides can also boost the production of hyaluronic acid in the skin, for a hydrated, plump and smoother skin.

In relation to the I.N.C.I. nomenclature, Greek qualifying prefixes are used. For instance, di-, tri-, tetra-, pentapeptides refer to peptides of 2, 3, 4, and 5 amino acids in length, and so forth. There are numerous variations: tetrapeptide-2, acetyl tetrapeptide-15, hexapeptide-2, acetyl tetrapeptide-9, alanyl glutamine, acetyl hexapeptide-1, carnosine, acetyl tetrapeptide-11, cyclopeptide-5, and so on...

Note : Peptides can have functions beyond their role in reducing the appearance of wrinkles. They can influence various biological processes in the skin such as inflammation, cell proliferation, melanogenesis, oxidative stress... When applied to hair follicles, certain peptides offer densifying properties. They stimulate, strengthen and densify the cells of eyelashes and eyebrows, while helping to keep them healthy.

• The oligopeptides provide trace elements to the skin to stimulate collagen production.

• The enzyme inhibiting peptides slow down the action of enzymes that degrade certain skin proteins such as collagen or glycosaminoglycans like hyaluronic acid.

• The signal peptides send messages to stimulate the production of certain proteins such as collagen, elastin, and hyaluronic acid.

• The neurotransmitter peptides are often compared to "botox" due to their inhibitory activity on the release of toxins that induce muscle contraction and expression lines.

Peptides are often identical or analogous to protein fragments already present in the body, which significantly reduces the risk of side effects. There are no contraindications to topical use of skincare products containing peptides; pregnant and/or breastfeeding women can use them. Furthermore, peptides are generally introduced into cosmetic formulas in very small quantities (which does not limit their biological actions in any way).

We have included pea peptides (INCI name: "Pisum Sativum (Pea) Peptide) in the following two treatments: the scalp serum densifying with 2% peptides and ginger extract (INCI name: "Zingiber Officinale (Ginger) Root Extract"), and the eyelash & eyebrow serum formulated with 2% pea peptides and castor oil (INCI name: "Ricinus Communis (Castor) Seed Oil"). The pea peptides are rich in phytonutrients, particularly in isoflavones. They stimulate, in the dermal papilla, specific molecules essential for reactivating the growth of hair, but also other types of hair such as eyelashes and eyebrows.

Furthermore, the density & firmness serum combines three peptides: cyclopeptide-5 (INCI name: "Cyclotetrapeptide-24 Aminocyclohexane Carboxylate"), acetyl tetrapeptide-11 and acetyl tetrapeptide-9. The 3 peptides present in this serum work simultaneously on different targets involved in the support and density of the skin. Acetyl tetrapeptide-9 acts on the lumican protein to strengthen the skin's structure. Acetyl tetrapeptide-11 acts on a protein present on the skin's surface to smooth it. The cyclo tetrapeptide-24 is an antioxidant and helps to combat free radicals.

The hyperpigmentation and firmness serum combines tranexamic acid at a high concentration (5%) with acetyl tetrapeptide-2, a multi-functional peptide, to reduce the appearance of pigmentation spots and firm the skin. The tetrapeptide-2 stimulates the synthesis of key molecules involved in skin support and firmness: elastin, collagen, and fibrillin. It also inhibits certain reactions in the melanogenesis process, thus reducing brown spots. Finally, it has a strong antioxidant power that protects the skin against free radicals and revives its natural glow.

Finally, ourwrinkle and blemish serum combines the densifying action of retinol (0.3%) with the anti-bacterial action of bakuchiol (1%) to reduce the appearance of wrinkles and correct blemishes. Synthesised by endemic Australian plants, it also containsplant-based polypeptides capable of working in synergy with retinol to promote the synthesis of type I collagen. They thus help to reduce the depth of wrinkles and densify the skin.

• BOREL J. P. & al. Stimulation of collagen synthesis in fibroblast cultures by a triterpene extracted from Centella asiatica. Connective Tissue Research (1990).

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

• SCHAGEN S. K Topical peptide treatments with effective anti-aging results. Cosmetics (2016).

• FERREIRA M. S. & al. Trending anti-aging peptides. Cosmetics (2020).

• PERLIKOWSKA R. Signal peptides - Promising ingredients in cosmetics. Current Protein & Peptide Science (2021).

• Dr. KRIVOSHIEV B. Peptides and proteins in cosmetics. Biorius.