Graphical abstract A critical review of the toxicity of one dimensional nanomaterials, with emphasize on carbon nanotubes is presented. The review focuses on the role of the size, aspect ratio, and mechanical properties on the toxicity of nanotubes and dissects the effect of the large lifetime of carbon nanotubes within cells and organisms. The figure provides a graphical representation of the three modes that describe the interaction between nanotubes and biological cells (in this case blood cells). The top panel describes the safe mode SM), the middle panel is representing the fakir mode (FM), and the bottom mode the impale mode (IM). To the left of each mode is shown qualitatively the stress (σ)–strain (ɛ) dependence for the cellular membrane with a localization of the mechanical domain associated to each mode. Highlights ► Reviews critically the toxicity and the risks of one dimensional nanomaterials. ► Investigates models/concepts about the toxicity of one dimensional nanomaterials. ► Discusses the connection between toxicity and carbon nanotubes retention. ► Reveals the combined effect of aspect ratio and mechanical properties. ► Suggests the role of partial phagocytosis.