Based on the physiological characteristic of tender

yin

in children， it is believed that

yin

deficiency serves as the internal core pathogenesis underlying recurrent psoriasis in children and constitutes the root cause of heat lingering in the blood system. Children with insufficient

yin

fluid tend to transform pathogenic

qi

into heat that invades the nutrient-blood systems after pathogens attack； moreover， latent pathogens in the blood level will flare up from interior to exterior when triggered by external pathogens， leading to recurrent psoriasis. The treatment focuses on the principle of expelling pathogens and nourishing

yin

with differentiated therapies. For initial pathogenic invasion progressing from exterior to interior and sinking into the

yin

aspect，

Yinqiao Decoction

（银翘汤） is applicable to expel pathogens and nourish

yin

， while

Huaban Decoction

（化斑汤） can clear heat from the

qi

level through the

ying

level； for latent pathogens complicated by deficiency， which is induced by external pathogens and transmits from blood to

qi

level when manifesting externally，

Xijiao Dihuang Decoction

（犀角地黄汤） is adopted to cool blood and expel macules， and

Huanglian Jiedu Decoction

（黄连解毒汤） to discharge heat and diffuse

qi

.