Abstract: Provided are a biological polysaccharide having the effect of preventing and treating acne and/or steroid-dependent dermatitis and the use thereof. Specifically, provided is the use of ?-glucan for preparing a formulation or composition, wherein the formulation or composition is used in the prevention and/or treatment of acne and/or steroid-dependent dermatitis. The ?-glucan has the effects of significantly relieving and improving acne and/or steroid-dependent dermatitis, effectively controlling the occurrence of acne and/or steroid-dependent dermatitis, accelerating the healing and/or regression of acne and/or steroid-dependent dermatitis.