Collagen is a large molecule, and the channels in the skin are small. As a result, collagen applied to the face is almost impossible to be absorbed by the epidermis.
Collagen is really important for human skin, supporting and keeping skin firm. However, as collagen is a large molecular structure, it cannot be directly absorbed by the body. It needs to be converted into amino acids through the digestive system, and then different kinds of amino acids are used to form different proteins for different parts of the body.
