Proteins are one of the basic elements of life and have diverse structural and functional roles in different organs and organ systems, including the skin. The three main structural proteins inside the skin are collagen, elastin and keratin.
Collagen is one of the most durable proteins in the body, is mainly composed of glycine, proline and hydroxyproline, and comprises more than 75% of the skin. In the body, collagen is produced by fibroblasts and this process is stimulated by ascorbic acid, acting as a cofactor in the process. It gives the skin its strength, waterproofing, and elasticity. When we are young, our skin is smooth and plump, which is due in large part to the presence of healthy collagen levels. As we get older there is decline in collagen production, which leads to the development of fine lines and wrinkles leading to change in the contour and appearance of the face. This forms the basis for use of ingredients that promote collagen synthesis or decrease its breakdown in anti-aging skin care products. Another function of collagen is in wound healing; it forms a mesh-like scaffold in the damaged tissue and seals off the wound by forming a scar.
Elastin is a protein within the elastic fibers of connective tissue and, as a component of the dermis, accounts for the elasticity of skin. It is composed of soluble tropoelastin, a ~65kDa protein that is highly cross-linked to form an insoluble complex and contains primarily, glycine and valine and modified alanine and proline residues. The most common interchain cross-link in elastins is the result of the conversion of the amine groups of lysine to reactive aldehydes by lysyl oxidase resulting in the spontaneous formation of desmosine cross-links. Elastin helps keep skin flexible but tight, providing a bounce-back reaction when pulled. It also helps keep skin smooth as it stretches during various activities like talking, laughing, smiling and eating. Elastin fiber breakdown due to UV damage, age or disease results in loss of elasticity and formation of fine lines and wrinkles. Keratin gives skin its strength and flexibility and waterproofs the skin surface.
Amino acids are the building blocks for proteins and, when applied topically, stimulate formation of collagen and elastin and promote cell renewal. Glutamine regulates acid-base balance and helps make the skin firm. Arginine plays an important part of the process of collagen synthesis. It is also thought to be necessary in stimulating protein synthesis and in accelerating the regenerative and restorative process of the skin. Cysteine makes up an essential component of hair, nails and the keratin of the skin. In skincare applications, this amino acid is particularly beneficial as it stimulates production of collagen, thereby promoting healthy and vibrant skin texture. Glycine makes up about one third of the proportion of collagen, which is essential for skin firmness and flexibility. Lysine is an important component of collagen in the skin, which is responsible for skin strength, suppleness and elasticity.