IL4 and major depressive disorder: In the present study, microglia activation in IMQ‐induced psoriasiform dermatitis mice was verified in the fields of hippocampus DG and cortex and substantial production of pro‐inflammation cytokines IL‐1β, IL‐6, and TNF‐α, while there was no significant difference in IL‐4 and IL‐10 expression levels, which further indicates that IL‐17A‐induced systemic inflammation can contribute to the development of a depressive‐like state, and in the pathological condition of psoriasis, systemic IL‐17A can trigger depression by mediating microglia M1 polarization and neuroinflammation.