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).
When E171 is part of a food product, it passes through the digestive system without causing harm because E171 combines with the other ingredients.
In a 2020 study published in the Journal of Trace Elements in Medicine and Biology, researchers conducted an in vitro experiment to analyze the effects of TiO2 nanoparticles on a human neuroblastoma (SH-SY5Y) cell line. The scientists evaluated “reactive oxygen species (ROS) generation, apoptosis, cellular antioxidant response, endoplasmic reticulum stress and autophagy.” The results showed that exposure to the nanoparticles “induced ROS generation in a dose dependent manner, with values reaching up to 10 fold those of controls. Nrf2 nuclear localization and autophagy also increased in a dose dependent manner. Apoptosis increased by 4- to 10-fold compared to the control group, depending on the dose employed.”
While the FDA maintains that the regulated use of titanium dioxide is safe, the European Food Safety Authority and some other experts warn of potential, serious health risks.