At the nanometer scale (about 50,000 times smaller than the width of a human hair), matter behaves in unusual ways: weak materials become strong, inert materials become active, and benign materials become harmful. In the same way that iron can be made into products as different as skillets and swords, the usefulness or harmfulness of nanotechnology products depends on how they are crafted at the nanometer scale.
然而纳米技术也在颠覆着我们对什么东西是有害的认识。在纳米范围（大约比人的头发丝的宽度小5万倍）上，物体的表现并不像寻常那样：弱的物质变强了，惰性的物质变得活跃了，而良性的物质变得有害了。以同样的方式铁可以被制造成像长柄平底煎锅和剑这样不同的产品，纳米技术产品的有用或有害完全要看它们在纳米范围上是怎样被制作的。其结果是，我们不能再依赖传统上单单根据原材料来界定危险的方式了。