Amino acids are important natural moisturizing factors (NMFs), that can be found naturally in the skin where they help the epidermis (upper layer of the skin) to stay nice and hydrated.
Amino acids are also the building blocks of proteins, such as collagen, so when you thoroughly chop up a big collagen molecule, you end up with an amino acid mixture, like this guy we are writing about. Btw, if you chop it up less thoroughly, you get hydrolyzed collagen, a kind of peptide mixture with smallish chains of amino acids.
Amino acids have low molecular weight (about 150 Da), so they can penetrate the upper layer of the skin where they help moisture retention and enhance the skin's suppleness and flexibility. In hair care, Collagen Amino Acids are able to improve shine, texture, and manageability of the hair.