Interleukin 4 (IL-4) can suppress delayed-type hypersensitivity reactions (DTHRs), including organ-specific autoimmune diseases in mice and humans. Despite the broadly documented antiinflammatory effect of IL-4, the underlying mode of action remains incompletely understood, as IL-4 also promotes IL-12 production by dendritic cells (DCs) and IFN-γ–producing T_H1 cells in vivo. Studying the impact of IL-4 on the polarization of human and mouse DCs, we found that IL-4 exerts opposing effects on the production of either IL-12 or IL-23. While promoting IL-12–producing capacity of DCs, IL-4 completely abrogates IL-23. Bone marrow chimeras proved that IL-4–mediated suppression of DTHRs relies on the signal transducer and activator of transcription 6 (STAT6)-dependent abrogation of IL-23 in antigen-presenting cells. Moreover, IL-4 therapy attenuated DTHRs by STAT6- and activating transcription factor 3 (ATF3)-dependent suppression of the IL-23/T_H17 responses despite simultaneous enhancement of IL-12/T_H1 responses. As IL-4 therapy also improves psoriasis in humans and suppresses IL-23/T_H17 responses without blocking IL-12/T_H1, selective IL-4–mediated IL-23/T_H17 silencing is promising as treatment against harmful inflammation, while sparing the IL-12–dependent T_H1 responses.