Beyond Microbeads: The Overlooked Occurrence and Co-occurrence of Synthetic Polymers in Leave-On Cosmetics

Abstract Synthetic polymers are widely used in leave-on cosmetic products, yet systematic product analyses of their occurrence across leave-on cosmetic categories remain limited. This study evaluated the occurrence and distribution of 17 targeted polymers across cosmetic products using ingredient-level analysis of large cosmetic datasets. Approximately 31% of products contained at least one targeted polymer; some contained multiple targeted polymers, with up to six identified in a single product. Our analysis revealed particularly high cumulative polymer frequencies in leave-on cosmetic products, including lip products (98.45) > eye makeup (97.73) > face makeup (67.96). Polyethylene and polybutene were prevalent in lip-related products, while carbomer and acrylate-based polymers dominated across skincare and makeup categories. Polylactic acid, polypropylene, and polystyrene had the lowest overall prevalence across the datasets. Co-occurrence analysis identified recurrent polymer pairings, particularly polyethylene with polybutene, and nylon-12 with methyl methacrylate crosspolymer, indicating recurring polymer combinations across products. Screening estimates suggested potential incidental oral polymer intake from lip products ranging from trace µg to >43 mg/day. The high prevalence of targeted polymers in leave-on products, particularly in categories associated with potential oral and dermal exposure, highlights an overlooked area in current discussions of synthetic polymer regulation and human exposure, and potential environmental release, which have historically focused primarily on rinse-off products and particulate microplastics.