This article first introduces the concepts that underlie the calculations of scattering and absorption of light by small particles. Results of Mie theory calculations of light scattering and light absorption by 20, 50 and 100 nm TiO2 and ZnO particles are then presented. As the attenuation, or extinction, by these particles is the sum of the scattering and absorption, the attenuation can then be calculated for wavelengths over the UVA and UVB region. These theoretical results are then shown to be in reasonable agreement with experimental results for alkyl benzoate dispersions of three different types of TiO2 particle whose mean sizes range from 35 to 145 nm. Finally, the link between these measurements and the absorption curves of formulated dispersions of sunscreens are demonstrated and related to in vitro SPF and UVAPF measurements.