Abstract: Porous cellulose microparticles and their use in, inter alias, cosmetic and pharmaceutic preparations are provided. These microparticles comprise cellulose I nanocrystals aggregated together, thus forming the microparticles, and arranged around cavities in the microparticles, thus defining pores in the microparticles. A method of for producing these microparticles is also provided. It involves mixing a suspension of cellulose I nanocrystals with an emulsion of a porogen to produce a mixture comprising a continuous liquid phase in which droplets of the porogen are dispersed and in which the nanocrystals of cellulose I are suspended; spray-drying the mixture to produce microparticles; and if the porogen has not sufficiently evaporated during spray-drying to form pores in the microparticles, evaporating the porogen or leaching the porogen out of the microparticles to form pores in the microparticles.