IL17A and psoriasis: Breakthroughs in the research of the pathogenesis of psoriasis have brought great benefits to patients with psoriasis, such as the research on the pathogenesis of psoriasis tumor necrosis factor‐α (TNF‐α), interleukin‐17 (IL‐17) and IL‐23 targeted biological agents have played an active role in the treatment of moderate to severe, refractory and special types of psoriasis.2