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 that contains both an amine group (-NH₂) and a carboxyl group (-COOH) bonded to the same carbon atom, to which a hydrogen atom and a variable side chain (R) are attached; this side chain determines the chemical properties of each amino acid. Of the approximately 500 amino acids known in nature, only 20 are found in the human body. These 20 assemble to form proteins or peptides. Nine of them must be obtained through the diet because the body cannot synthesize them. These are called essential amino acids.

The use of peptides in cosmetics dates back almost half a century. The first ones were animal-derived, obtained by protein hydrolysis, such as keratin, collagen, or elastin, derived from feathers, skins, or animal tissues. These processes yielded heterogeneous mixtures of peptide fragments, varying in chain length and amino acid composition. Despite their lack of specificity, these peptides were widely used for their moisturizing properties and low cost under the INCI names Hydrolyzed Collagen, Hydrolyzed Keratin or even Hydrolyzed Silk.

In the 1990s, the mad cow disease crisis profoundly challenged the use of animal-derived ingredients. This era marked the shift toward laboratory-designed synthetic peptides. However, their initial efficacy remained limited because their hydrophilic nature prevented penetration through the skin barrier. A decisive breakthrough occurred when researchers grafted a fatty acid onto the peptide chain, giving rise to lipopeptides. This modification enabled improved transdermal absorption. From the 2000s onward, these advances propelled peptides to the status of major active ingredients in cosmetic formulations.

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

• Oligopeptides.

  Oligopeptides are very short fragments composed of two to ten amino acids. They can be associated with trace elements such as copper, zinc, or manganese, forming metallic peptide complexes capable of enhancing the enzymatic processes involved in skin repair. These peptides particularly promote the synthesis of collagen and elastin while also stimulating fibroblast proliferation, thereby contributing to improved skin firmness and elasticity. One of the most well-known oligopeptides is copper tripeptide-1 (GHK-Cu), recognized for its wound-healing effects.

• Enzyme-inhibitory peptides.

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

• Signal peptides.

  Also called biomimetic peptides, they mimic the natural signals sent by the skin when it sustains injury or stress. These peptides directly stimulate fibroblasts to produce more collagen, elastin, and glycosaminoglycans such as hyaluronic acid. For example, palmitoyl pentapeptide-4 is one of the most extensively studied signaling peptides and is known for its ability to promote dermal regeneration and reduce the appearance of wrinkles.

• Neurotransmitter peptides.

  Often compared to a milder 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 best-known is argireline, or acetyl hexapeptide-8, which helps smooth tension areas such as the forehead or eye contour without fully blocking muscle mobility.

The peptides are attracting growing interest in cosmetics due to their numerous beneficial effects on the skin.

• Peptides can target skin aging.

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

• Peptides mitigate oxidative stress.

  The oxidative stress results from an imbalance between the production of free radicals and the skin’s ability to neutralize them. These unstable free radicals can react with skin components—such as the dermal structural proteins—and alter them, thereby accelerating skin laxity. Certain peptides exhibit antioxidant properties that may help prevent this phenomenon. For example, carnosine can neutralize free radicals and limit lipid peroxidation within cellular membranes. Their effectiveness depends on their molecular structure: peptides rich in hydrophobic amino acids like leucine, alanine, or proline, or in aromatic residues such as tryptophan or histidine, have an enhanced capacity to donate electrons to free radicals.

• Peptides can accelerate skin healing.

  Some peptides, such as LL-37, can participate in skin repair. They exert an immunomodulatory effect that balances inflammatory responses and creates an environment conducive to tissue regeneration. Studies on human fibroblasts have shown that these peptides activate the transcription of genes involved in proliferation, such as KI67, and in cell migration, such as CXCR4, two key 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 signaling pathway, which is known to promote angiogenesis.

• Peptides can support skin hydration.

  Some biomimetic peptides actively support skin hydration by enhancing water retention in the epidermis. In a 30-day clinical study involving 20 women, a hydrogel enriched with SH-oligopeptide-2, SH-polypeptide-1, SH-oligopeptide-1, and SH-polypeptide-42 was evaluated. The results showed an average hydration increase of 13.8% after 30 minutes, rising to 17.5% after one hour, compared with 9.7% for the placebo. These biomimetic peptides also improved skin elasticity, underscoring their overall efficacy.

• Peptides exhibit a soothing potential.

  Certain peptides are particularly beneficial for sensitive or reactive skin, thanks to their ability to modulate inflammation and reinforce 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 for skin cohesion, like 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 daily comfort.

• Peptides have antimicrobial effects.

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

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

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

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

The peptides are introduced into cosmetic formulations at very low concentrations, sufficient to exert a biological effect without posing any 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 visible irritation, toxicity, or 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 essential to remember that each skin type can respond differently to cosmetic treatments. Therefore, it is advisable to perform a preliminary test on a small area of skin—such as the inner elbow or the wrist—to verify that you are not sensitive to peptides.

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