Because of their small size, nanoparticles may have unique physical and chemical properties. These properties may cause them to interact with living systems differently than larger materials with the same chemical composition (also known as bulk materials).

The US and Canada, however, approve the use of titanium dioxide as a food additive. Canada's recent review of titanium dioxide reconfirmed its safety and pointed out that many of the toxicity studies the EU reviewed were not relevant to the safety of titanium dioxide as a food ingredient, and that the ban is based on an abundance of caution and uncertainty.