This in vitro study found that negatively charged SiO2 nanoparticles suppressed antigen-induced degranulation and activation-marker changes in IgE-sensitized mouse bone marrow-derived mast cells. By contrast, mTiO2 nanoparticles showed cytotoxic and pro-inflammatory effects, including enhanced DNP-induced IL-6 release, suggesting nanoparticle composition can shape early allergic immune responses.