The theory of the ‘IL-23/T helper 17 (IL-23/Th17) pathway’ in the pathogenesis of psoriasis, which Kastelein et al. and Fitch et al. identified and proposed in 2007, remains the foundational theory in psoriasis pathogenesis research and a significant target for pharmaceutical development (6, 9, 10). This evidence concerns the gene IL23A and psoriasis.