Anti-allergic drugs, also called antihistamines, are divided into two types, one is H1 receptor blockers, which are mainly distributed in the skin, mucous membranes, blood vessels and brain tissue. The other is H2 receptors, which are mainly distributed in the mucosa of the digestive tract. h1 receptor antagonists, which are divided into one generation and two generations. First-generation antihistamines, which are commonly used paracetamol, diphenhydramine, promethazine, ketotifen, cyproheptadine, but their main side effects, is easy to cross the blood-brain barrier, easy to produce weakness, drowsiness, dizziness, lack of concentration, some of them also have anticholinergic effects, including urination difficulties. Therefore, they need to be banned or used with caution by fine workers and drivers who work at height, such as those with glaucoma and cataracts and prostate enlargement. Second-generation antihistamines, including fexofenadine, loratadine, cetirizine, imipramine, etc., are absorbed more quickly orally. Their biggest advantage is that they are not easy to pass the blood-brain barrier and have less impact on the central nervous system. They can be taken orally once a day and are more suitable for drivers, people working at height and long-term users.