Benign by design: A paradigm shift in cosmetic ingredient development

Concerns about the environmental impact of cosmetic ingredients are growing among consumers worldwide. These substances, that is, the constituents of cosmetics, are entering wastewater as well as household waste after use, and many of these molecules are not removed during sewage treatment or degraded in the environment, leading to environmental persistence. Addressing this challenge requires intervention at the earliest stages of cosmetic ingredient development, designing them to be biodegradable when released into the environment. This review aimed to provide an overview of the benign by design (BbD) strategies available to improve the biodegradability of chemicals, demonstrating their applicability to cosmetic ingredients. The BbD strategies encompass de novo design, creating novel compounds from scratch, or the re-design by modifying existing molecules highlighting how biodegradability can be enhanced while maintaining, or potentially improving, functional performance. The strategies can be non-targeted or targeted, following a series of rules of thumb, and applying experimental and in silico tools. Overall, the presence of alkyl linear chains and functional groups such as hydroxyl, carbonyl, ester, amide or carboxylic acid groups favours biodegradation, whereas the presence of alicyclic rings and highly branched alkyl chains, halogens, nitro, nitroso or azo groups hinders biodegradability. The review shows that BbD strategies, already applied in pharmaceutical and chemical design, are equally relevant for the design of cosmetic ingredients to avoid environmentally persistent ingredients, such as per- and polyfluoroalkyl substances (PFAS) and silicones. Beyond reducing environmental persistence, the integration of BbD strategies into cosmetic ingredient development supports the transition towards a greener and more sustainable cosmetic industry, contributing to the preservation of natural resources. This also opens new opportunities for innovation within an expanded and environmentally conscious chemical design space.