Conventional sunscreen formulations are limited by post-application epicutaneous penetration that increases the risk of allergic dermatitis, cellular damage, and filter photodegradation upon ultraviolet radiation (UVR) exposure. We developed a new approach for UV protection that eliminates penetration into the skin: encapsulation of organic UV filters into bioadhesive nanoparticles (BNPs).1 The BNPs are produced from a block copolymer of poly(lactic acid) and hyperbranched polyglycerol (PLA-HPG).2 BNPs form stable aqueous suspensions, facilitate adherence to the stratum corneum without subsequent intra-epidermal penetration, and are water-resistant on skin yet can be removed via active towel drying. We show that BNP-based sunblock significantly reduces double-stranded DNA breaks in skin cells when compared to a commercial sunscreen formulation.1 To develop these BNPs into a sunscreen that provides broad-spectrum UVR protection, we assessed the capacity of BNPs for co-incorporation of UV filters avobenzone (AVO) and octocrylene (OCR). The ratio of UV filters within nanoparticles was optimized for broad spectrum UVA and UVB absorbance, filter-filter stabilization upon UV irradiation, and maximum drug loading. In vitro water-resistance tests showed significant topical particle retention on synthetic skin at 85% over 3 hrs. In a pilot clinical study, protection against UVR-induced erythema of BNPs was found to be comparable to the FDA standard P2. Thus, sunscreen formulations utilizing BNP incorporation of combinations of organic filters may offer key safety and performance advantages.6 In addition to protection against UV damage to skin, the PLA-HPG nanoparticles that we have developed may have advantages for other consumer and pharmaceutical applications.