Sericin

Sericin is a silk-derived protein used as a film-former and conditioning/humectant ingredient, typically included at low percentages in moisturizers and hair/skin conditioners. While generally well-tolerated and not an intrinsically irritating “active,” protein-based materials can provoke irritation or sensitization in a small subset of highly reactive or atopic patients, especially on compromised barrier skin. Given this nonzero allergy/irritation potential despite common cosmetic use, I rate it as gentle rather than exceptionally gentle. Safety Notes: In commercial skincare and haircare, sericin (silk protein) is most often used at very low levels (~0.01–0.1%) as a film-forming/conditioning additive in moisturizers, serums, shampoos, and conditioners, consistent with typical supplier use-level guidance and INCI placement low in the list. Higher-strength consumer products marketed as “silk protein/sericin” masks, ampoules, and repair treatments can reach ~1–5% active sericin (especially in leave-on masks/serums or intensive rinse-off treatments), with levels above this becoming uncommon due to viscosity/film feel, solubility/processing constraints, and cost; no specific global maximum is set, so the observed upper end is driven by formulation practicality rather than regulation.