Specific information about the particle size distribution, agglomeration state, morphology and chemical composition of four silica samples, used as additives in food and in personal care products were achieved with a combination of analytical techniques. The combined use of differential centrifugal sedimentation (DCS), sedimentation field flow fractionation (SdFFF), scanning and transmission electron microscopy (SEM and TEM) allows to classify the water dispersed samples as “nanomaterials” according to the EC definition. The mechanical stirring and the ultrasound treatment were compared as dispersion methods. The particles surface chemical composition determined by Particle-Induced X-ray Emission (PIXE) and X-ray photoelectron spectroscopy (XPS) assessed the different level of purity between the pyrogenic and the precipitated silica and highlighted particles surface chemical composition modifications in the outer shell when dispersed by mechanical stirring. The potential toxic effects of silica on intestinal Caco-2 cells were investigated using MTS assay and by measuring lactate deshydrogenase (LDH) release and caspases 3/7 activity after 24h of incubation. No or limited decrease of cell viability was observed for all particles regardless of dispersion procedure suggesting a relative innocuity of these silica samples.