Background and Purpose: Titanium dioxide (TiO2) has several unique properties, including as an opacifier, pigment, and ultraviolet blocker, and is widely used in paints, cosmetics, personal care products, food products, and pharmaceuticals. The use of TiO2 as a food additive has historically been considered safe. In recent years, however, the safety of food-grade TiO2 has come into question due to the presence of nanoscale (<100 nm) particles and toxicology studies suggesting a potential for immunotoxicity, neurotoxicity, and genotoxicity. In 2021, the European Food Safety Authority (EFSA) updated a safety assessment of TiO2 (E171) and concluded that E171 could no longer be considered safe as a food additive, primarily due to a concern for genotoxicity. In 2022, Health Canada reported that the studies EFSA relied upon in their re-evaluation did not represent TiO2 as a constituent in foods and concluded that there was not enough information to warrant a more cautionary approach for TiO2 in foods. Similarly, the Food and Drug Administration (FDA) concluded that the available studies do not demonstrate safety concerns related to the use of TiO2 as a color additive. Considering the proposed Adverse Outcome Pathways (AOP) for oral exposure to TiO2 particles, our objective was to evaluate existing in vivo toxicology studies for No Observed Adverse Effect Levels (NOAELs) or Lowest Observed Adverse Effect Levels (LOAELs) of key event (KE) effects along the AOP and compare these threshold events to estimated human daily TiO2 exposures from various food substances. Methods: An AOP for carcinogenicity from oral exposure to TiO2 has been proposed to include 1) cellular uptake in the intestine, 2) reactive oxygen species generation, 3) oxidative stress, 4) persistent inflammation/epithelial injury, 5) DNA damage, 6) epithelial cell proliferation, and 7) preneoplastic epithelial lesions leading to intestinal adenomas/carcinomas. A systematic evaluation of available in vivo toxicology studies was conducted to identify NOAELs and LOAELs of KEs along the AOP following oral administration to TiO2. Additionally, the physicochemical properties of TiO2 used in each study, including its crystal structure, size and size distribution, and charge, were recorded to evaluate its similarity to TiO2 E171. Daily human exposures to TiO2 were estimated based on reported analytical TiO2 concentrations in different food products (e.g., chewing gum, candy, chocolate) and the daily human consumption patterns of each food product from What We Eat in America, the dietary interview component of the National Health and Nutrition Examination Survey (NHANES). Results: Available data show that TiO2 used in most in vivo studies is not representative of foodgrade TiO2. Further, most in vivo studies included routes of administration not relevant to human dietary exposure (e.g., oral gavage) and were administered in stable, homogenized suspensions of ultrasonically dispersed particles. However, in vivo studies that specifically evaluated the toxicological effects of E171 reported NOAELs that were up to thousands of times greater (depending on the KE stage) than the mean daily oral intake of TiO2 from various food products in individuals of different age groups in the United States. Other in vivo studies that evaluated different forms of TiO2 according to Organization for Economic Co-operation and Development (OECD) guidelines reported NOAELs with similar patterns compared to the mean daily oral intake of TiO2 in individuals of various age groups. Further, a two-year rodent bioassay conducted by the National Toxicology Program (NTP) found no evidence of intestinal tumors or other intestinal lesions in rats or mice fed a form of TiO2 consistent with the current forms used in foods. Available studies also showed no general and organ toxicity or reproductive and developmental toxicity. Conclusions: Comparing the NOAELs of AOP KE effects to estimated human TiO2 exposures from different food products suggest that the precursor threshold events (e.g., oxidative stress, inflammation, epithelial injury) along the proposed AOP are unlikely to occur at TiO2 doses in a typical human diet. Studies that evaluated relevant forms of TiO2 did not observe adverse effects at levels up to thousands of times greater than what the average consumer ingests from different food substances. As such, toxicological evidence of KE along the proposed AOP for oral exposure to TiO2 E171 as a food additive does not support a risk to human health