Nanoparticles can enter cells actively or passively and can trigger various effects. These effects are often coupled with the formation of free radicals, which can be released within the cell or produced on the surface of the particles. Free radicals can induce inflammation, cell death and DNA damage and thus impair human health. The threshold value, i.e. the amount of incorporated nanomaterials that causes an effect, remains unknown. Based on present knowledge, there are no known nanoparticle-specific cellular reactions. However, it is only the knowledge of basic cellular processes that allows us to understand the magnitude of an induced effect,. This, in turn, is a prerequisite for testing drugs and administering medicines. This dossier is therefore designed to provide an overview of selected cell functions. By examining the relevant functional and molecular pathways, we can better understand how nanoparticles potentially cause damage.