How long it takes for the rash caused by taking cephalosporin allergy to subside is related to the severity of the allergy and the treatment measures taken after the allergy, and needs to be analyzed on a case-by-case basis. Patients with rashes caused by taking cephalosporin allergy should immediately stop taking cephalosporin drugs. If the allergic rash is mild, you can choose to take levocetirizine hydrochloride or loratadine, and at the same time apply topical glycolate lotion or boric acid solution to enhance care, and the rash can generally subside in a few hours to two weeks. If the allergic rash is heavy and causes exfoliative dermatitis, on the basis of basic anti-allergic treatment, glucocorticoids can be chosen, combined with calcium gluconate and vitamin C intravenous application, if necessary, hospitalization is required, but the specific rash remission time is determined by the effect of treatment. In addition, during anti-allergy treatment, patients need to keep the rash area dry and clean, ensure sufficient rest time and adequate nutrition supply to help the recovery.