The present invention is about a pharmaceutical composition, an oral preparation, and an injection preparation containing a G protein-coupled Receptor19 (GPCR19) agonist, specifically sodium taurodeoxycholate(HY2191) and its derivative, as an active ingredient for preventing or treating allergic skin diseases. The present invention is also about an external preparation and a cosmetic composition containing said pharmaceutical composition for preventing and improving allergic skin diseases. The said pharmaceutical composition shows an excellent efficacy in treating and improving allergic dermatitis compared with the steroid ointments or immunosuppressive ointments currently used. The said pharmaceutical composition reduces the level of serum IgE, which is a major factor causing allergic dermatitis, increases TH1 cytokine alleviating allergic dermatitis and reduces TH2 cytokine that exacerbates allergic dermatitis. The said pharmaceutical composition also reduces infiltration of a mast cell, eosinophil, and neutrophil in dermis and ameliorates clinical symptoms such as erythema, hemorrhage, edema, excoriation, erosion, scaling and dryness. Thus, the said pharmaceutical composition can be used to prevent and treat allergic skin diseases.
