Nanopollution. Artwork showing nanoparticles (in small circles at right) attacking neurons (nerve cells, green). At left is a profile view of a human head and shoulders, showing that nanoparticles could be ingested or inhaled, and a possible location of neuron damage in the brain. The structures in the two red circles are fullerenes, molecules made from an allotrope of carbon. The bottom circle represents semiconductor molecules. The exact risks of nanoparticles to health is unknown, but due to their small size they are able to cross biological membranes to enter organs and cells. Studies on fish and insects have shown that exposure to fullerenes can cause brain damage, but no such research has been carried out in mammals.