The building blocks of our skin, common amino acids include: arginine, aspartic acid, cysteine, cystine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine, and valine. If you see an ingredient ending in -ine, there's a good chance it's an amino acid. Each amino acid has slightly different functions, ranging from antioxidants to collagen synthesis to tissue repair (source). Some can even act as a penetration enhancer, helping other ingredients go deeper within our skin (source).
While amino acids are found naturally in our bodies or in our food, there has been research to design modified amino acids that provide greater hydration levels than hyaluronic acid (source), so it'll be exciting to see this new development applied to skin care!