Relative to a lot of other things that people should be concerned about, titanium dioxide in my mind, is really low on the list. I would be more worried about some substitutes that people are using for titanium dioxide that don't have decades of research associated with it, said Westerhoff.

In a study published in the journal Environmental Toxicology and Pharmacology in 2020, researchers examined the effects of food additives titanium dioxide and silica on the intestinal tract by grouping and feeding mice three different food-grade particles — micro-TiO2, nano-TiO2, and nano-SiO2.  With all three groups, researchers observed changes in the gut microbiota, particularly mucus-associated bacteria. Furthermore, all three groups experienced inflammatory damage to the intestine, but the nano-TiO2 displayed the most pronounced changes. The researchers wrote: “Our results suggest that the toxic effects on the intestine were due to reduced intestinal mucus barrier function and an increase in metabolite lipopolysaccharides which activated the expression of inflammatory factors downstream. In mice exposed to nano-TiO2, the intestinal PKC/TLR4/NF-κB signaling pathway was activated. These findings will raise awareness of toxicities associated with the use of food-grade TiO2 and SiO2.”

Matthew Wright, chair of the authority's working group on titanium dioxide, noted that the evidence for general toxic effects was not conclusive, but that the panel couldn't rule out genotoxicity entirely. There were also some current data limitations and the assessment could not establish a safe level for daily intake of the food additive, he stated.