Diphenhydramine is an antihistamine, which is what we commonly call an anti-allergy drug. It is an antihistamine H1 receptor acting drug and belongs to the class of amino ethers. It has a strong inhibitory effect on the central nervous system and will also have the effects of atropine drugs, such as dry mouth and suppression of the nervous system. It is usually used in allergic diseases of the skin and mucous membranes, such as urticaria and allergic rhinitis, and also in the prevention of motion sickness. Diphenhydramine is mainly used for acute allergic reactions, but it can also be used for sedation and hypnosis, because it has a certain inhibitory effect on the center, and it may be used to assist in the administration of anesthesia, such as the administration of drugs before anesthesia. For example, it can be used for skin and mucous membrane allergic reactions, such as vulvar itching and some drug rashes, in addition to urticaria and allergic rhinitis, as mentioned earlier, all have very good effects. However, there are contraindications to its use, such as newborns, premature babies and women during pregnancy are prohibited, as well as patients suffering from angle-closure glaucoma.