Everything you need to know about peptides in cosmetics.

Peptides are short chains of amino acids linked together by peptide bonds. An amino acid is an organic molecule bearing both an amine group (-NH₂) and a carboxyl group (-COOH) attached to the same carbon atom, together with a hydrogen atom and a variable side chain (R), which determines the chemical properties of each amino acid. Of the approximately 500 amino acids known in nature, only 20 occur in the human body. These assemble to form proteins or peptides. Nine of them must be obtained through the diet, as the body cannot synthesise them. These amino acids are known as essential.

The use of peptides in cosmetics dates back almost half a century. The first ones were of animal origin, obtained by protein hydrolysis, such as keratin, collagen or elastin, sourced from feathers, hides or animal tissues. These processes produced heterogeneous mixtures of peptide fragments, whose composition varied in size and amino acid composition. Despite their lack of specificity, these peptides were widely used for their moisturising properties and low cost, under the INCI names Hydrolyzed Collagen, Hydrolyzed Keratin or even Hydrolyzed Silk.

In the 1990s, the “mad cow” crisis profoundly questioned the use of animal-derived ingredients. This period marked a turning point towards synthetic peptides developed in the laboratory. However, their initial efficacy remained limited, as their hydrophilic nature prevented their penetration through the skin barrier. A decisive advance occurred when researchers grafted a long-chain fatty acid onto the peptide backbone, giving rise to lipopeptides. This modification enabled significantly improved trans-epidermal absorption. By the 2000s, these breakthroughs had elevated peptides to major active ingredients in cosmetic care.

There are several families of peptides used in cosmetics, each targeting different biological processes.

• Oligopeptides.

  Oligopeptides are very short chains composed of two to ten amino acids. They can bind to trace elements such as copper, zinc or manganese, forming metallopeptide complexes that enhance the enzymatic processes involved in skin repair. These peptides particularly stimulate the synthesis of collagen and elastin while stimulating fibroblast proliferation, thereby contributing to improved firmness and elasticity of the skin. One of the best-known oligopeptides is copper tripeptide-1 (GHK-Cu), recognised for its wound-healing effects.

• Enzyme-inhibiting peptides.

  These peptides act by slowing the activity of enzymes responsible for the breakdown of the skin’s structural components, such as matrix metalloproteinases (MMPs), elastase and hyaluronidase. By limiting the degradation of collagen, elastin and hyaluronic acid, these enzyme-inhibitory peptides help to maintain the skin’s density and suppleness.

• The signal peptides.

  Also known as biomimetic peptides, they mimic the skin’s natural signalling when it undergoes injury or stress. These peptides directly stimulate fibroblasts to produce increased collagen, elastin and glycosaminoglycans, such as hyaluronic acid. For instance, palmitoyl pentapeptide-4 is one of the most extensively studied signalling peptides and is known for its ability to enhance dermal regeneration and diminish wrinkles.

• Neurotransmitter peptides.

  Often regarded as a gentler alternative to botox, neurotransmitter peptides inhibit the release of acetylcholine at nerve endings, thereby reducing the micro-contractions of facial muscles responsible for expression lines. The most well-known is argireline, or acetyl hexapeptide-8, which helps to smooth tension-prone areas such as the forehead or eye contour without fully blocking muscle mobility.

Peptides are attracting increasing interest in cosmetics due to their numerous benefits for the skin.

• Peptides can target skin ageing.

  Peptides limit the onset of wrinkles at various levels. Some, such as palmitoyl tripeptide-1 (Pal-GHK) and palmitoyl pentapeptide-4 (Pal-KTTKS), directly stimulate fibroblast activity, promoting the production of collagen, elastin and glycosaminoglycans to reinforce skin structure and suppleness. Others, such as palmitoyl tripeptide-3/5, mimic extracellular matrix proteins, thereby both enhancing collagen synthesis and curbing its degradation. Finally, neurotransmitter-inhibitor peptides, such as argireline, act on acetylcholine release to reduce the muscle contractions responsible for expression lines, thus providing a smoothing effect.

• Peptides mitigate oxidative stress.

  The oxidative stress resulting from an imbalance between the production of free radicals and the skin’s ability to neutralise them. Unstable, these free radicals can react with skin components, such as structural proteins in the dermis, for instance, and alter them, thus accelerating skin laxity. Certain peptides possess antioxidant properties that may be valuable in preventing this phenomenon. Indeed, carnosine, for example, can neutralise free radicals and limit lipid peroxidation within cell membranes. Their efficacy depends on their molecular structure: peptides rich in hydrophobic amino acids such as leucine, alanine or proline, or aromatic residues such as tryptophan or histidine, have a greater capacity to donate electrons to free radicals.

• Peptides can accelerate skin wound healing.

  Certain peptides, such as LL-37, can be involved in skin repair. They exert an immunomodulatory action that balances inflammatory responses and creates an environment favourable to tissue regeneration. Research conducted on human fibroblasts has shown that these peptides activate the transcription of genes involved in proliferation, such as KI67, and in cell migration, such as CXCR4, two important steps in the process of wound healing. Other peptides, such as hBD-2 and hBD-3, support skin repair by activating the FGFR1/JAK2/STAT3 signalling pathway, known to favour angiogenesis.

• Peptides can support skin hydration.

  Certain biomimetic peptides actively contribute to skin hydration by promoting water retention in the epidermis. A 30-day clinical trial conducted on 20 women evaluated a hydrogel enriched with SH-oligopeptide-2, SH-polypeptide-1, SH-oligopeptide-1 and SH-polypeptide-42. The results revealed an average increase in hydration of 13.8% after 30 minutes, rising to 17.5% after one hour, compared with 9.7% for the placebo. These biomimetic peptides also enhanced skin elasticity, emphasising their comprehensive action.

• Peptides have a soothing potential.

  Certain peptides are particularly beneficial for sensitive or reactive skin, thanks to their ability to modulate inflammation and strengthen the skin barrier. Acetyl dipeptide-1 cetyl ester is a prime example: it acts on the POMC gene pathway, stimulating the production of endogenous peptides such as α-MSH, which is known to regulate inflammatory responses. It also enhances the expression of genes essential to skin cohesion, including aquaporin-3 and filaggrin, while reducing the synthesis of prostaglandin E2, a mediator involved in redness and irritation. These combined actions contribute to the skin’s day-to-day comfort.

• Peptides exhibit antimicrobial activity.

  Certain peptides exhibit antibacterial properties, which can be particularly useful for preventing blemishes. Peptides such as P156, derived from the phage lysin Prevotella intermedia (PlyPi01), have shown targeted activity against Cutibacterium acnes and Staphylococcus aureus, two bacteria involved in acne-related skin inflammation. If these effects were confirmed in vivo, owing to their antibacterial and anti-inflammatory properties, these peptides could be promising additions for blemish-prone skin.

They are primarily known for their effects on the skin, peptides can also be used to care for hair. They are reported to influence growth. A study in mice showed that daily administration over six weeks of a marine collagen peptide (500 mg/kg body weight) could activate the Wnt/β-catenin and GSK-3β/β-catenin pathways, known to regulate the hair growth cycle. An increase in the expression of the growth factors IGF-1 and VEGF, essential to the vascularisation of hair follicles, was also observed. However, apart from the fact that this study was conducted in a murine model, it is based on oral administration of peptides rather than on topical application. Further work is still needed to confirm that peptides stimulate hair growth.

Peptides are also credited with a restorative effect on the hair fibre. A study investigated peptides derived from fish skin for repairing damaged hair strands. An emulsion was formulated, applied to the various strands, and the researchers evaluated the repair using microscopic, spectroscopic and calorimetric analyses. The results showed a 5.94% increase in the α-spiral structure of keratin and a 28.44% rise in helical content, reflecting improved stability and a structure closer to that of healthy hair. Moreover, total and hydrophobic amino acid levels increased by 16.77 g/100 g and 2.47 g/100 g respectively, confirming enhanced hair strength. In addition, microscopic observations revealed that the disordered cuticles of damaged hair became noticeably smoother after using the peptide emulsion.

Topical peptides generally exhibit no contraindications and can be used by all individuals, including pregnant or lactating women.

Peptides are introduced into cosmetic formulations at very low concentrations, sufficient to exert a biological effect without posing a risk to the skin. Current research indicates that the majority of topical peptides are safe, with a low risk of irritation, toxicity or allergic reactions. For example, Peptide 14, a senotherapeutic peptide designed to reduce senescent cells in the skin, was tested on human skin models and in a patch test with 54 participants. The results showed no irritation, toxicity or visible skin reaction. Additional tests conducted ex vivo confirmed the absence of genotoxicity, and even human fibroblasts and keratinocytes exposed to the peptide at concentrations up to 100 μM remained viable and non-toxic.

However, it is important to remember that each individual’s skin can react differently to cosmetic treatments. It is therefore recommended to perform a preliminary patch test on a small area of skin, such as the inner elbow or the wrist, to ensure that you are not sensitive to peptides.

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