AbstractGenistein is applied worldwide as an alternative medicament for psoriasis (Ps) because of its anti-inflammatory activity and perceived beneficial impact on the skin. Hereby, we report our in vivo and in vitro investigations to supplement scientific research in this area. The reduction of clinical and biochemical scores in mild to moderate Ps patients taking genistein, its safety, good tolerability with no serious adverse events or discontinuations of treatment, no dose-limiting toxicities, negligible changes in pharmacodynamic parameters and remarkable serum interleukin level alterations were documented in this study. A certain regression of the Ps phenotype was visible, based on photo-documented Ps lesion evaluation. Through in vitro experiments, we found that genistein reduced IL-17A and TNF-α induced MAPK, NF-κB, and PI3K activation in normal human epidermal keratinocytes. Moreover, at the mRNA level of genes associated with the early inflammatory response characteristic for Ps (CAMP, CCL20, DEFB4A, PIK3CA, S100A7, and S100A9) and key cellular signalling (MTORC1 and TFEB), we showed that this isoflavone attenuated the increased response of IL-17A- and TNF-α-related pathways. This allows us to conclude that genistein is a good candidate for Ps treatment, being attractive for co-pharmacotherapy with other drugs.