Titanium dioxide has long been used as a food coloring additive, but at the beginning of 2020 France became the first country in the world to ban the compound being used for this purpose. Over recent years many global companies have moved to stop using titanium dioxide as a food additive amidst growing concerns over its safety, however, it still can be found in hundreds of foods.

Much of the current debate over the safety of titanium dioxide as a food additive revolves around particle size. The majority of titanium dioxide particles used in food additives are relatively large – over 100 nanometers (nm) in diameter – so most toxicology research has focused on the health effects of consuming those larger particles.

More recent study has suggested titanium dioxide nanoparticles (those particles less than 100 nm in diameter) may be more bioactive, with a greater propensity to induce adverse effects compared to larger particles. One analysis of titanium dioxide particles used as food additives found 36 percent of particles were less than 100 nm in diameter.

"The bigger particles won't be absorbed easily, but the smaller ones could get into the tissues and accumulate somewhere," says Hang Xiao, lead author on the new study.