Silk Amino Acids — Frequently Asked Questions

By molecular weight, which determines what they do. Silk amino acids are fully hydrolysed to individual free amino acids, typically under 200 daltons, and act as humectants that bind water and penetrate the hair cuticle. Silk peptide is only partially hydrolysed, leaving short chains that can deposit and form a film. The INCI name is the same for both, so molecular weight must be specified.

Because a free amino acid has no chain to entangle with its neighbours. Film formation depends on molecules long enough to overlap and interact on a surface, which is what gives peptides their substantivity and smoothing effect. Amino acids are too small for that, so they act by binding water and by penetrating rather than by coating.

Repair and strengthening claims, because their small size allows them to penetrate the cuticle and reach the cortex rather than sitting on the surface. That matters in damaged and chemically treated hair, where protein has been lost from the fibre itself. They are also used in skin care as humectants.

Predominantly glycine, alanine and serine, which together make up the great majority of silk fibroin. That composition, dominated by small amino acids with simple side chains, is what allows silk protein to pack into the tight ordered structure that gives the fibre its strength, and it is what the hydrolysed material delivers.