Assessment of skin sensitization potential is mandatory for ingredients dedicated to topical applications. A battery of in vitro tests covering the key steps of the Adverse Outcome Pathway (AOP) for skin sensitization has been recommended to replace animal testing. However, despite international guidelines on in vitro methods, there is no universal approach defining their combination. The purpose of this work was to assess skin sensitization of botanical ingredients relying on a previously developed in vitro testing strategy. This tool focused on complex and poorly water-soluble substances, which were not already covered. Sixteen botanical extracts were tested in a sequential approach, starting with Sens-Is, supplemented by Organization for Economic Cooperation and Development (OECD) in vitro methods when necessary. The results on the selected well-known botanical sensitizers complemented the relevance of the strategy. Testing on experimental botanicals could detect skin sensitizers. In addition, phytochemistry was a determining support to identify and remove the components at the origin of the effect. Altogether, these results enlarged the scope of the methodology to various ingredient categories and chemical natures, contributing to place on the market new ingredients, safe for workers and end-users.

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.