Itchy plaster may be drug allergy, may also be contact dermatitis and other diseases. 1. Drug allergy: mainly allergic to the drug ingredients in the ointment, mostly considering the patient is allergic to the population. If the patient is in the state of viral infection, autoimmune diseases and other diseases, the incidence of drug allergy is higher. Common drugs include antipyretic and analgesic, anesthesia and so on. The patient’s skin will appear itchy, erythema, wind masses and other manifestations, and at the same time there will be chest tightness, shortness of breath, wheezing and other systemic symptoms. 2. Contact dermatitis: this disease is mainly due to skin contact with exogenous substances, causing stimulation caused by allergic reactions. If the patient is allergic to the colloid on the ointment, it is easy to itch, erythema, edema and other symptoms when applying the ointment. To summarize, patients with itchy plasters need to go to the hospital in time to improve the examination and clarify the specific causes, so as not to delay the condition.