Keratin is a structural protein that is naturally associated with the hair fibre. In this kind of rinse-off mask it mainly works on the outside of the hair, coating and conditioning the surface so strands feel less coarse and look more even. It does not rebuild the hair from the inside; the effect is a cosmetic surface improvement.
Arginine is an amino acid often used in hair cosmetics. Its job here is to help maintain a better conditioned feel and improve slip. Slip is the glide you feel when you run a comb or your fingers through the hair, and more slip means easier detangling with less pulling.
Biotin, also known as vitamin B7, is included in many hair products aimed at brittle-looking, tired lengths. In topical formulas it is valued as part of a strengthening and smoothing blend.
Together, these three ingredients support the mask's main purpose: making lengths feel more supple, look shinier, and detangle more easily after washing and styling. The formula conditions the surface and reduces the rough texture on damaged lengths, but it does not alter the natural structure of the hair fibre.