There are many reasons for red patches on the body, which may be caused by allergic reactions, infectious diseases, psoriasis, etc. Usually, it is necessary to make a clear diagnosis first and then give targeted treatment. 1. Allergic reaction: allergic to the surrounding environment or diet, medication and other factors, can cause skin erythema, accompanied by itchy symptoms, the patient can be detached from the allergen, to avoid re-exposure to such substances, and at the same time oral antihistamine drugs such as loratadine for treatment. 2. Infectious diseases: Infectious diseases of soft tissues of the skin can cause local inflammatory redness and swelling, usually accompanied by local pain and burning sensation, such as boils, carbuncles, reticular lymphadenitis, which can be treated with topical antibiotic ointment, such as erythromycin ointment, etc. If the symptoms are aggravated, the patient can also take antibiotic medication orally. 3. Psoriasis: commonly known as “psoriasis”, typically manifested as limited or generalized scaly erythema or plaque, aggravated in autumn and winter, relieved in summer, at this time should consult a doctor in a timely manner, to clarify the diagnosis, comply with the doctor’s instructions for standardized treatment, and should not be unauthorized use of medication. There are many other reasons why there are red patches on the body, and it is recommended that patients seek timely medical attention to clarify the cause of the disease and then carry out regular treatment.