Amino acids are the small building blocks that make up peptides, and proteins. Each amino acid has a unique structure, and as such plays a specific role within the body. There are around 20 different types considered to be most important for human health. In the outer layer of the skin, the stratum corneum, they are present in the ‘natural moisturising factors’, our skin’s own moisturising mechanism, and they help to support water transport between skin cells to keep our surface smooth and hydrated.