(A) Allergic diseases have typically been inversely related to the risk of glioma development, and (B) conversely, positively related to the risk of neurological or psychiatric diseases. (C-F) An extended knowledge of allergy’s impact on the brain was unearthed using rodent models of allergic disorders. (C) These studies demonstrated that allergic inflammation could increase the level of mRNA and cytokines from Th1/Th2 immunity, (D) as well as of IgE and IgG in brain lysates compared to controls. In parallel, allergic inflammation was shown to lead to activation of brain-specific cells, such as (E) microglia and (F) astrocytes. (G) Changes in the resting state of spontaneous brain activity demonstrate allergic inflammation can modulate brain homeostasis in humans. Created with « BioRender.com».