Background: The research team previously found that interleukin-19 (IL-19) was associated with atopic dermatitis (AD) by single-cell RNA sequencing. However, little is known about its cellular sources, targets, functions, and underlying mechanisms. Objective: This study investigated the roles and mechanisms of IL-19 in AD. Methods: The role of IL-19 in AD was analysed in skin lesions and serum samples of patients with AD, IL-19 knockout (IL-19 KO) mice and immortalized human keratinocyte cell line (HaCaT) cells stimulated with different inflammatory factors. Results: The expression of IL-19 significantly increased in skin lesions of patients with AD and the MC903-induced AD mouse model, with keratinocytes (KCs) identified as the primary source. Notably, the expression of IL-20Rα/IL-20Rβ receptor subunits varied across different skin regions. IL-19 knockout mice exhibited significantly lower severities of dermatitis and eosinophil infiltration in the ear compared with wild-type mice. Mechanistic investigations revealed that upregulation of IL-19 in AD exacerbated the dysfunction of KC by promoting the phosphorylation of STAT (signal transducer and activator of transcription axis) 3 and STAT6, specifically characterized by reduced production of barrier proteins and increased secretion of epithelial-derived pro-inflammatory factors. Additionally, IL-19 was found to promote Th2/Th17 polarization of CD4+ T cells and increase M2 macrophage markers. Finally, IL-19 amplified IL-4/IL-13 biological effects as a cofactor. Conclusion: Overall, this study was the first to outline the cell-specific role of IL-19 in AD and the potential for targeting IL-19 in the treatment of both immune and non-immune cell-mediated inflammation in AD.