Peptides and proteins have become increasingly significant ingredients in cosmeceutical formulations, particularly those aimed at addressing the signs of skin ageing and improving skin health. While often used interchangeably by consumers, it is important to distinguish between these molecules. Peptides are short chains of amino acids, while proteins are larger, more complex structures composed of longer polypeptide chains. Both play crucial roles in the body’s physiological functions, and specific sequences of amino acids in peptides can act as biologically active communication tools that direct skin functioning.
The use of peptides in cosmeceuticals is driven by their potential to target specific skin mechanisms. Engineered peptides, designed with specific amino acid sequences, can mimic or modulate the activity of naturally occurring peptides, leading to various benefits such as stimulating collagen and elastin production, reducing the appearance of wrinkles, inhibiting melanin synthesis, and promoting skin repair. Many peptides with “anti-aging” properties have been developed and incorporated into skincare products.
However, the incorporation of peptides into cosmetic formulations presents several challenges. These hurdles include skin penetration, stability, potential toxicity, analytical methods, and cost.
Skin Penetration: The stratum corneum, the outermost layer of the skin, acts as a significant barrier to the penetration of many substances, including peptides. Peptides, even small ones, tend to be hydrophilic and may carry an electrical charge, which hinders their ability to pass through the lipid-rich stratum corneum to reach the viable epidermis and dermis where they need to exert their effects. While the stratum corneum itself is not the primary target for most peptides, they need to reach living skin cells to deliver their message. Larger peptides and proteins face even greater challenges in penetrating the skin barrier due to their size.
Stability: Peptides can be susceptible to degradation by enzymes present on the skin or within the formulation itself. Their stability can also be affected by factors such as pH, temperature, and the presence of other ingredients in the product. Maintaining the integrity and bioactivity of peptides within a cosmetic formulation throughout its shelf life is crucial for efficacy.
Toxicity: While generally considered safe for topical application, the potential for skin irritation or sensitisation with certain peptides cannot be entirely ruled out and needs to be assessed during product development.
Analysis: Quantifying and verifying the presence and integrity of specific peptides within a complex cosmetic matrix can be analytically challenging, requiring sophisticated techniques such as liquid chromatography-mass spectrometry (LC-MS/MS).
Cost: The synthesis of specific peptide sequences can be expensive, which can impact the overall cost of the final cosmetic product.
To overcome the skin penetration barrier, various formulation strategies have been employed. One common approach is attaching a lipophilic chain, such as a fatty acid, to the peptide. This modification can increase the peptide’s affinity for the lipid components of the stratum corneum, thereby enhancing its penetration. For instance, palmitoyl-carnosine has shown improved penetration compared to unmodified carnosine. However, this technique may have limitations for longer peptide chains and could potentially interfere with the peptide’s biological activity.
Other strategies to enhance transcutaneous delivery include the use of amphiphilic cell penetration peptides (CPPs), attaching a poly-arginine chain to the peptide, and designing hyaluronic acid (HA) conjugates. CPPs can facilitate the transport of molecules across cell membranes. HA conjugates may help in both hydration and penetration enhancement. Liposome formulations, which are small vesicles composed of lipid bilayers, may also aid in carrying peptides through the skin barrier, although published data in this specific area for cosmetics may be limited.
Proteins, due to their large size, generally do not penetrate the skin barrier effectively and primarily function on the skin surface. Structural proteins like collagen, elastin, and keratin, when used in cosmetics, primarily provide moisturising and film-forming benefits. The use of animal-derived structural proteins declined significantly due to concerns like bovine spongiform encephalopathy (BSE), but is slowly making a comeback.
Enzymes, a class of functional proteins, are also used in cosmetic products. These can have various actions, such as proteolytic enzymes for exfoliation or enzymes with antioxidant or DNA repair functions. Enzyme function is highly specific and relies on their precise amino acid sequence and three-dimensional structure. In conclusion, peptides represent a valuable category of active ingredients in cosmeceuticals due to their ability to target specific skin functions. While proteins largely exert their effects on the skin surface, specific peptides offer the potential for more targeted action within the skin. Overcoming the challenges associated with peptide formulation, particularly skin penetration and stability, remains a key focus of research and innovation in cosmetic science. As our understanding of skin biology and peptide mechanisms continues to advance, the development of even more effective and specific peptide-based cosmeceuticals is anticipated.