A nanometer is a thousandth of a micron and a micron is a thousandth of a millimeter, so a nanometer is a millionth of a millimeter or 10-9 meters. To be classified as a nanomaterial (NM), the material must be less than 100 nm in size in at least one direction. The  International Standards Organization (ISO) does not distinguish between engineered nanoparticles and naturally occurring nanoparticles. There are naturally occurring nanoparticles in the environment today.

While nanomaterials present seemingly limitless possibilities, they bring new challenges to understanding, predicting, and managing potential safety and health risks to workers.  The National Institute for Occupational Safety and Health (NIOSH) is the leading federal agency conducting research and providing guidance on the occupational safety and health implications and applications of nanotechnology.