Objective To investigate the effects of Shechuangzi San on Th1/Th2 immune function in eczema rats and analyze its mechanisms in treating eczema.Methods Fifty SD rats were randomly divided into blank group,model group,Shechuangzi San high dose group,Shechuangzi San low dose group,and Bingbaiye liquid group,with 10 rats in each group.The rat eczema model was established using 2,4-dinitrochlorobenzene.The blank group and model group were topically treated with 0.9%saline,the Shechuangzi San high dose group was topically treated with a decoction of Shechuangzi San at a concentration of 2.32 g·mL-1,and the low dose group was topically treated with a decoction of Shechuangzi San at a concentration of 1.16 g·mL-1.And the Bingbaiye liquid group was topically treated with the original liquid of Bingbaiye,once in the morning and once in the evening,for a total of 14 days.After the last administration,the skin lesions on the rats'backs were observed and the skin lesion scores were evaluated.The pathological changes of eczema lesions were observed by HE staining,and semi-quantitatively scored.ELISA method was used to detect the levels of IFN-γ,IL-4,IL-18,and IL-33 in rat serum.Flow cytometry was used to determine the Th1/Th2 ratio in the serum.Results Compared to the blank group,the rat skin lesion score in the model group was significantly increased(P<0.05),with a series of skin lesions including edema,erythema,scaling,lichenification appearing on the back.Pathological sections showed excessive keratosis,thickening of cuticular layer,edema of epidermis sponge,infiltration of a large number of inflammatory cells in epidermis,and the semi-quantitative score of skin lesions was significantly increased(P<0.05).Serum levels of IL-4,IL-18,and IL-33 were significantly increased(P<0.05),while the level of IFN-γ was significantly decreased(P<0.05).Serum Th1/Th2 ratio decreased(P<0.05).Compared to the model group,the rat skin lesions in the Shechuangzi San high and low dose groups and the Bingbaiye liquid group were significantly improved(P<0.05),Pathological sections showed that the structure of epidermis was restored to normal,the cuticle became thinner,the spongy edema of epidermis disappeared,epidermal inflammatory cells disappeared,and the semi-quantitative score of skin lesions decreased(P<0.05).Serum levels of IL-4,IL-18,and IL-33 were decreased(P<0.05),while the level of IFN-γ was increased(P<0.05),serum Th1/Th2 ratio increased significantly(P<0.05).and the therapeutic effect of the Shechuangzi San high and low dose groups was superior to that of the Bingbaiye liquid group(P<0.05).Conclusion Shechuangzi San can effectively improve the skin lesions of rats with eczema,repair the pathological damage of skin lesions,and reduce the levels of inflammatory factors.Its mechanism may be related to the inhibition of secretion of inflammatory factors such as IL-4,IL-18,and IL-33,promotion of IFN-γ release,and restoration of Th1/Th2 imbalance.