Diphenhydramine is an antihistamine and has some therapeutic effect on allergic reactions. In addition, it has a strong inhibitory effect on the central nervous system and also has antiemetic and anti-infective effects. It is mainly used to treat allergic diseases, including type I-IV allergic reactions, such as allergic rhinitis, allergic eczema, angioneurotic edema, and allergic drug rash. In addition, it has some sedative and tranquilizing effects and can be used for pre-surgical administration. It also has some anti-parkinsonism and drug-induced extravertebral symptoms, and some anti-dizziness and anti-emetic effects. Diphenhydramine cream can be used topically for the treatment of neurodermatitis and itchy skin.