Abstract Though it has been claimed that nanotechnology has great potential for cleaner technology, caution is required as to application of nanoparticles (<100 nm). Studies relevant to human exposure have shown that nanoparticles can be hazardous. Manufactured nanoparticles may also have ecotoxicological effects after discharge into water. There is a case to limit human exposure to nanoparticles originating in production. As traditional ‘end-of-pipe’ technology has limited effectiveness in capturing nanoparticles, source reduction is important for the limitation of exposure during production. With regard to products, it seems important to distinguish between applications that are inherently dispersive and applications that are not inherently dispersive. In case of dispersive applications, alternatives and ‘built in’ hazard reduction merit consideration. Hazard reduction may be possible by e.g. limiting biopersistence, arranging for low toxicity of degradation products or surface modification. When nanoparticles are applied in a way that is not inherently dispersive, controlling the size of particles that originate due to cleaning, wear, tear and corrosion is important.