Erythema of large skin areas may be related to allergic factors, such as eczema and medicinal rashes, or to other diseases, such as ringworm. 1. Eczema: the cause may be related to heredity, hormone level changes, immune abnormalities and other factors. Patients will have symptoms such as erythema, papules and edema, and the rash can be distributed in any part of the body. 2. Drug rash: the cause of the disease is mainly related to drug factors, the patient’s skin will appear asymmetric red patches, which may be accompanied by itching. 3. Tinea corporis: the cause of the disease is mainly related to the pathogenic fungal infections such as Trichophyton rubrum and Trichophyton purpureum. Patients will have red scaly patches, papules, blisters and other symptoms, and when the condition is serious, the lesions may be widely distributed. If the skin grows into a large area of erythema, it is recommended to go to a regular hospital for consultation and examination, to clarify the cause of the disease, and to carry out treatment under the guidance of the doctor.