A red rash is considered to be the cause of eczema, urticaria and rubella, which can be treated by applying medication as well as taking oral medication. 1. Eczema: an inflammation of the skin caused by a variety of internal and external factors. It is related to the patient’s exposure to allergic substances, which will trigger an inflammatory reaction in the body, resulting in a red rash all over the patient. It can be treated by applying glycerin lotion and compound dexamethasone cream. 2. Urticaria: Urticaria is related to physical stimulation and mental stress, which can lead to a red rash on the skin, and with further aggravation of the condition, there will be wind clouds of different sizes, accompanied by angioedema. You can take antihistamines, such as cetirizine hydrochloride tablets, loratadine tablets and so on. 3. Rubella: Rubella is usually caused by rubella virus infection, belongs to the infectious disease, will lead to the patient all over the red rash, there will be obvious itching, with the further aggravation of the disease, will lead to the patient to appear cough, sore throat. You can take ibuprofen extended-release capsules and diclofenac sodium extended-release tablets as prescribed by your doctor. A red rash may also be other diseases such as pityriasis rosea, patients need to go to a professional skin hospital and follow the doctor’s instructions for treatment. All of the above drugs should be used under the guidance of a doctor.