[en] Electron irradiated poly(methyl methacrylate) (PMMA) and polystyrene (PS) nanoparticles as alternatives to existing sunscreen active ingredients which have safety controversies have been studied. The electron irradiation produces chromophores so that the irradiated polymers turn capable of absorbing ultraviolet (UV) rays. UV-Vis spectroscopy indicates a significant increase in the absorbance in the spectral range of UV and a redshift of the absorption edge is observed at a higher electron fluence. Results of FTIR and Raman studies imply chemical alterations of the irradiated polymers, elucidating the creation of UV absorbing properties. According to results of in vitro 3T3 neutral red uptake (NRU) phototoxicity test in compliance with OECD TG 432, the irradiated PMMA was classified as a non-phototoxic material. In addition, in vitro sun protection factors (SPFs) of formulations containing irradiated polymer nanoparticles in various electron fluence were determined according to ISO 24443. In this study, the effects of electron irradiation and the characteristics of the irradiated polymers are discussed