This thesis describes the characterization and photochemical behavior of metal oxide nanopigments derived from commercial sunscreens. We investigate their size, morphology, elemental composition, and crystal structure using electron microscopy, x-ray diffraction and energy dispersive x-ray spectroscopy. TiO2 and ZnO nanoparticles are known to exhibit photochemistry in their pure form. We report the reactivity of derived materials towards Congo red, and spin trap electron paramagnetic resonance spectroscopy. The results of this work have implications for regulation of nanotechnology in consumer products. Currently nanoscale TiO2 and ZnO can be legally added to sunscreens without any requirement that their size be disclosed on the product labels. Our results reveal that these sunscreen components can be photoactive, resulting in the degradation of Congo red dye and generation of hydroxyl radicals. These observations warrants a reexamination of the policy that holds nanoscale materials identical to their bulk counterparts for labeling purposes.