Psoriasis vulgaris is notoriously difficult to treat and prone to recurrence. Traditional Chinese medicine （TCM）， however， has shown considerable efficacy in mitigating or suppressing such recurrence. The underlying reason lies in the TCM concept of "latent pathogens"， which are prone to be reactivated by external pathogenic factors， thereby triggering relapse. At the early stage of recurrence， manifestations of "latent fire" often appear externally. If treatment is not thorough， the condition may shift into a state of "stalemate between healthy Qi and pathogenic factors"， in which the disease appears on the skin but is rooted in deeper pathological layers， remaining unresolved and accumulating internally. Over time， blood stasis arises from fire， and the fire further congeals due to stasis， leading ultimately to recurrent flare-ups. This aligns with the modern immunological concept of "immunological memory" mediated by tissue-resident memory T cells （T_RM） in the skin， which corroborates the TCM view of "latent fire inducing blood stasis". The interaction between T_RM and keratinocytes （KC） parallels the entanglement of latent fire and latent stasis， both of which are deeply entrenched and difficult to resolve. The core pathogenesis of recurrent psoriasis vulgaris lies in "latent fire causing blood stasis". The hallmark is the deep concealment and persistence of latent fire and stasis， which linger and await an opportunity to reemerge. Based on this understanding， Xijiao Dihuangtang is employed to cool the blood， resolve stasis， and eliminate latent pathogens， and treatment is tailored according to the disease stage through three-phase syndrome differentiation. In the progressive stage， both exterior and interior are treated， with emphasis on clearing latent fire. In the stationary stage， the focus shifts to dispelling latent stasis and simultaneously regulating the Zang-fu organs. In the regressive stage， efforts are made to prevent the retention of latent pathogens and to strengthen healthy Qi. Accordingly， drugs effective in dispersing wind and clearing heat， pungent-moistening and dredging the collaterals， and tonifying deficiency and moistening dryness are often employed to achieve optimal outcomes. The precise mechanisms by which Xijiao Dihuangtang treats recurrent psoriasis vulgaris remain to be fully elucidated. Current research suggests it may intervene in the recurrence process through inhibiting KC proliferation via the PI3K/Akt/mTOR signaling pathway and glycolysis， regulating the Th1/Th2 and Th17/Treg cell balances to restore immune homeostasis， suppressing inflammatory cytokine production to alleviate the inflammatory response， modulating angiogenesis-related factors， such as vascular endothelial growth factor A （VEGF-A） and matrix metalloproteinase-9 （MMP-9）， to control disease progression， and restructuring the gut microbiota to modulate systemic immunity and thereby influence the course of disease recurrence.