Sudden allergic itching is usually caused by contact with unknown allergic substances that produce an allergic reaction, which can be regulated by general treatment, topical medication, oral medication and other measures. 1. General treatment: relax, avoid mental stress, drink more water to promote metabolism, eat a light diet, avoid scratching the skin, avoid eating suspicious food or contacting suspicious allergenic substances. 2. Topical medication: use glycerine lotion, compound dexamethasone ointment, tretinoin cream and other drugs for treatment. 3. Oral medicine: you can take cetirizine, chlorpheniramine and other antihistamines, and in severe cases, you can also cooperate with prednisone, dexamethasone and other glucocorticoid drugs. Suddenly allergic to itching, need to go to the regular hospital in time for examination, follow the doctor’s instructions standardized treatment.