Clinically, there is no such thing as a fourth generation of antiallergic drugs. In medical practice, there are four main categories of drugs currently used for anti-allergy, antihistamines, leukotriene receptor blockers, allergic reaction mediator blocking and releasing agents, and glucocorticoids. 1. Antihistamines: divided into the first generation and the second generation, the first generation is mainly paracetamol, phenylephrine, etc., and the second generation is mainly loratadine, cetirizine, etc. The main function is to antagonize histamine. The main effect is to antagonize histamine H1 receptor, inhibit vascular exudation, reduce tissue edema. 2. Leukotriene receptor blockers: mainly montelukast, zalukast, etc. Leukotriene is an important chemical mediator of allergic reactions, blocking leukotriene receptors can interrupt the chain of allergic reactions, thus inhibiting allergic reactions. 3. Allergic reaction mediator blocking and releasing agents: mainly ketotifen, doxepin, not only can inhibit the release of allergic reaction mediators, but also H1 receptor blocking effect. 4. Glucocorticoids: mainly hydrocortisone, dexamethasone and so on. Glucocorticoids can stabilize the cell membrane, but also improve vascular permeability, with anti-inflammatory and reduce the role of exudation. If there is any discomfort, timely consultation is recommended.