What are peptides and what are their uses in cosmetics?

Peptides are small-sized proteins.They are composed ofchains of amino acids (aa)linked together viapeptide bonds. The use of peptides in skincare is beneficial when the production of collagen in the skin slows down. Indeed, these proteins promote the synthesis of collagen to prevent skin sagging and ageing.

Peptides are categorised into four groups based on their biological actions:

• Signal peptides (e.g.: acetyl tetrapeptide-9, acetyl tetrapeptide-11, palmitoyl tripeptide-1, cyclopeptide-5, etc...): As soon as they embed themselves into the skin pores, these peptides stimulate the synthesis of collagen, elastin and glycosaminoglycans in the dermis. These actions promote skin firmness.

• Enzyme inhibiting peptides (e.g.: acetyl tetrapeptide-2, pea peptides, etc...): These peptides block undesirable enzymes such as tyrosinase (an enzyme that stimulates melanin production) to ensure the skin is radiant and even. They also slow down the enzymatic process that breaks down collagen.

• Neurotransmitter inhibiting peptides (e.g. acetyl hexapeptide-8, etc...): Once released into the skin, this category of peptides relaxes the muscles to reduce expression wrinkles and fine lines. They are often compared to "botox" due to their inhibitory activity on the release of toxins that induce muscle contraction.

• Carrier peptides (e.g.: copper tripeptide-1, etc...): As their name suggests, they optimise the transport of essential trace elements through the skin cells. Carrier peptides release copper or magnesium to stimulate the skin's bioactive molecules and promote the healing process.

When applied topically, exogenous peptides induce changes in the complex pathways that regulate 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 provide suppleness 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.

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

Regarding 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 plenty of variations: Acetyl Tetrapeptide-15, Hexapeptide-2, Acetyl Tetrapeptide-9, Alanyl Glutamine, Acetyl Hexapeptide-1, Acetyl Tetrapeptide-11, Carnosine, Cyclotetrapeptide-24 Aminocyclohexane Carboxylate.