Silk proteins: fibroin and sericin
Two proteins from the same cocoon with different jobs. Fibroin is the structural fibre, sericin the glue that holds it — and sericin is the more interesting one for skin.
What is Silk proteins: fibroin and sericin?
Silk cocoons are made of two proteins. Fibroin is the structural core fibre, a highly crystalline protein of large molecular weight. Sericin is the gum surrounding it, and is conventionally discarded in silk processing — which is why it became available cheaply as a cosmetic ingredient. Both are used hydrolysed in skincare.
What each does
Fibroin forms smooth, flexible films and is valued for the surface feel it gives and for its biocompatibility; it is also studied extensively as a biomaterial scaffold. In skincare its contribution is largely film-forming and sensory, with moisture retention as a consequence.
Sericin is more biologically interesting. It is rich in serine and other hydroxy amino acids, giving it strong water-binding capacity, and it has been studied for reduction of transepidermal water loss, antioxidant activity and effects relevant to atopic and dry skin conditions. Where a silk claim has substance, sericin usually carries it.
Where does Silk proteins: fibroin and sericin appear in the range?
Vegalab's Age Repair and Hyaluronic Skin Repair NanoSerums both use fibroin and sericin, described together as a silk-protein resilience complex. The pairing is sensible: fibroin for film and feel, sericin for hydration and antioxidant contribution.
What does Silk proteins: fibroin and sericin not do?
Neither penetrates to the dermis or contributes to your own structural proteins. Silk protein does not tighten skin in any lasting sense — the immediate smoothing is a film effect that washes off. And silk is an animal-derived material, which matters for readers who care about that.