What are the risks of nanotechnology?

well people think that the nanoparticles will turn into self replicating nanorobots. but that is not true. in actual fact there are no risk except the fact that scientists say if they do put them into somones body and design them so they can eg, cure an illness. well scientist think that the nanomachines might when travelling in your body somehow go into your brain and damage it big time. but we have still got years to find out yet.