The skin is the largest organ that separates our body from the outside world and is constantly exposed to pathogens and antigens. Therefore, various immune cells are present in the skin, and the interaction of these cells induces dermatitis in response to foreign antigens. For example, inflammation is induced by Th1 cells in viral infection and contact dermatitis, Th2 cells in atopic dermatitis, and Th17 cells in psoriasis. Antigen-presenting cells (APCs) act as a bridge between innate and adaptive immunity and play an important role in driving T cell-mediated cutaneous responses. Currently, the heterogeneous human cutaneous APC population is incompletely characterized, and its contribution to these diseases remains unclear. Therefore, we performed single-cell RNA sequencing of inflammatory skin disease to identify the all-APC subsets, including the several novel APC fractions. LAMP3+ activated dendritic cells (DCs) were increased in atopic dermatitis and psoriasis and produced IL-15. DC3 were increased only in psoriasis and produced IL-1B and IL-23A, essential for psoriasis development. TREM2-positive macrophages were increased in granulomatous diseases. Single-cell RNA sequencing allows for a detailed classification of APCs, which will help elucidate the pathogenesis at the single-cell level.