Animal-Free Skin Sensitization Testing: In Chemico and In Silico Integrated Approach

The increasing prohibition of animal testing for cosmetic products has driven the development of alternative approaches to ensure consumer safety. Skin sensitization is one of the most critical toxicological endpoints to evaluate, requiring rigorous assessment to ensure the safety of cosmetic ingredients. This study proposes an Integrated Testing Strategy (ITS) that combines in chemico (Direct Peptide Reactivity Assay—DPRA) and in silico approaches (a six-platform computational panel) to evaluate the sensitization potential of substances. Initially, the in chemico methodology was validated through a partial proficiency demonstration to ensure experimental reliability. Subsequently, this ITS was applied to the Baccharis trimera extract and its major marker, 3-Caffeoylquinic acid (chlorogenic acid/3-CQA). Our results demonstrate that the DPRA alone is insufficient to classify the sensitization potential of complex mixtures, as recommended by OECD guidelines. The integration of in silico data proved essential to interpret the reactivity of the botanical matrix, revealing that the sensitization potential observed in the extract does not stem solely from 3-CQA, but likely results from the synergistic contribution of more lipophilic caffeoylquinic acid isomers. This approach demonstrates that integrating experimental and computational methods is fundamental for a robust safety assessment, offering an efficient, animal-free strategy for the early screening of cosmetic ingredients and for refining the interpretation of toxicological data in complex chemical environments.