In food, titanium dioxide is often used as an artificial color additive. Tasha Stoiber, senior scientist at the consumer health nonprofit Environmental Working Group, says titanium dioxide can generally be thought of as a paint primer – it often goes on a hard-shelled candy like Skittles before the color is added to give it a uniform shine.

In a study published in the journal Food and Chemical Toxicology in 2016, researchers investigated whether titanium dioxide exposure led to an increase in colorectal tumor creation in mice by using a colitis associated cancer model. By measuring tumor progression markers, the researchers found that mice given titanium dioxide experienced enhanced tumor formation in the distal colon.  There was also a decrease of cells that act as a protective barrier in the colon. The researchers wrote: “These results suggest that E171 could worsen pre-existent intestinal diseases.”