A circle of red skin usually may be pityriasis rosea, annular polymorphic erythema, ringworm, specific analysis is as follows: 1, pityriasis rosea: mainly oval-shaped erythema, with fine scales on it, the first start a large erythema, after which can be scattered distribution of small erythema, accompanied by a certain itching, the disease is mainly related to viral infection or swimming and other factors; 2, annular polymorphic erythema: manifested as annular erythema, the center slightly receding, mainly due to infection, drug allergies and other factors, in clinical treatment can be applied to the application of dinaide ointment; 3, ringworm: mainly due to fungal infection caused by the skin disease.