Hydrogenated Castor Oil/Sebacic Acid Copolymer

Hydrogenated Castor Oil/Sebacic Acid Copolymer is a high–molecular weight film-forming/emollient polymer used primarily as a texture/viscosity modifier in leave-on products, typically at low percentages, and it is not an acid active at skin pH. Available safety/patch-test data for similar castor-oil–derived polymers and sebacic acid copolymers suggest low irritation potential, with reactions being uncommon and usually related to individual sensitivities rather than inherent irritancy. Given use on compromised skin in some formulations and the need to protect highly reactive eczema patients, I score it as very gentle but not fully inert due to rare idiosyncratic reactions. Safety Notes: In commercial skincare and color cosmetics this polymer is most often used as a structuring/film-forming rheology modifier, where it appears at low levels (~0.1–1%) in emulsions and serums to improve slip and stability. Higher levels (5–15%) are observed in anhydrous sticks, balms, and long-wear film-forming products where it functions as a primary gellant/structurant. The upper end (~20–25%) is seen in high-structure consumer-available balm/stick formats (leave-on), while rinse-off products typically sit at the low end due to cost and limited need for strong film/structure.