Applicability Domain of the Sens-Is In Vitro Assay for Testing the Skin Sensitization Potential of Rheology-Modifying Polymers

Assessing the propensity of ingredients to induce skin sensitization through in vitro testing is crucial for worker and consumer safety. This is particularly important for novel and high-performance ingredients with complex structures, such as rheology-modifying polymers, which are extensively used in cosmetics, pharmaceuticals, and detergents. The Sens-Is assay has proven effective in distinguishing skin sensitizers from non-sensitizers for difficult-to-test ingredients when integrated into a multi-method in vitro approach. Therefore, the primary goal of this research was to explore whether the Sens-Is in vitro assay is suitable to evaluate rheology-modifying polymers. Fifteen structurally diverse rheology-modifying polymers, including natural polymers obtained by extraction, chemical synthesis, or biotechnology, spanning varying physical forms and concentrations, were evaluated. The results showed that most polymers were non-sensitizing, consistent with available in vivo data. Although polymer macromolecules generally exhibit limited skin sensitization potential due to their surface confinement, the Sens-Is assay permitted the detection of weak signals from secondary components or possible byproducts in specific cases. This work confirms Sens-Is as a useful tool in an overall approach to assessing the skin sensitization liability of polymers under development, but careful solvent selection is crucial to ensure accurate results and prevent potential overexposure due to polymer retention on the epidermal surface.