Nanomaterials present new challenges to understanding, predicting and managing potential health risks. They may interact with the human body in different ways than more conventional materials, due to their extremely small size. For example, studies have established that the comparatively large surface area of inhaled nanoparticles can increase their toxicity. Such small particles can penetrate deep into the lungs and may move to other parts of the body, including the liver and brain. There are still many knowledge gaps to be filled before we fully understand how to work safely with these materials. Until these and other research questions are answered, it is prudent to proceed with caution when working with nanomaterials.