BACKGROUND: The increasing prevalence of food sensitivities has been attributed to changes in gut microenvironment; however, ubiquitous environmental triggers such as inorganic nanoparticles (NPs) used as food additives have not been thoroughly investigated. OBJECTIVES: We explored the impact of the NP-structured food-grade silicon dioxide (fg-SiO2) on intestinal immune response involved in oral tolerance (OT) induction and evaluated the consequences of oral chronic exposure to this food-additive using a mouse model of OT to ovalbumin (OVA) and on gluten immunopathology in mice expressing the celiac disease risk gene, HLA-DQ8. METHODS: Viability, proliferation, and cytokine production of mesenteric lymph node (MLN) cells were evaluated after exposure to fg-SiO2. C57BL/ 6J mice and a mouse model of OT to OVA were orally exposed to fg-SiO2 or vehicle for 60 d. Fecal lipocalin-2 (Lcn-2), anti-OVA IgG, cytokine production, and immune cell populations were analyzed. Nonobese diabetic (NOD) mice expressing HLA-DQ8 (NOD/DQ8), exposed to fg-SiO2 or vehicle, were immunized with gluten and immunopathology was investigated. RESULTS: MLN cells exposed to fg-SiO2 presented less proliferative T cells and lower secretion of interleukin 10 (IL-10) and transforming growth factor beta (TGF-b) by T regulatory and CD45+ CD11b+ CD103+ cells compared to control, two factors mediating OT. Mice given fg-SiO2 exhibited intestinal Lcn-2 level and interferon gamma (IFN-c) secretion, showing inflammation and less production of IL-10 and TGF-b. These ellects were also observed in OVA-tolerized mice exposed to fg-SiO2, in addition to a breakdown of OT and a lower intestinal frequency of T cells. In NOD/DQ8 mice immunized with gluten, the villus-to-crypt ratio was decreased while the CD3+ intraepithelial lymphocyte counts and the Th1 inflammatory response were aggravated after fg-SiO2 treatment. DISCUSSION: Our results suggest that chronic oral exposure to fg-SiO2 blocked oral tolerance induction to OVA, and worsened gluten-induced immunopathology in NOD/DQ8 mice. The results should prompt investigation on the link between SiO2 exposure and food sensitivities in humans. https://doi.org/10.1289/EHP12758