Pleural effusions are divided into leaky, which is caused by increased microvascular pressure or decreased osmotic pressure, and exudative, which is caused by increased permeability of the pleural surface to proteinaceous fluid due to pleural inflammation. Lymphatic obstruction can also cause accumulation of pleural fluid. There are many causes of exudative and leaky effusions. In a normal person, there is 3-15 ml of fluid in the pleural cavity, which acts as a lubricant during respiratory movements, but the amount of fluid accumulation in the pleural cavity is not constant. Even in a normal person, 500-1000 ml of fluid is formed and absorbed every 24 hours. The pleural cavity is reabsorbed from the venous end of the capillaries, and the rest of the fluid is recycled to the blood by the lymphatic system. If the dynamic balance is disrupted by systemic or local lesions, the formation of fluid in the pleural cavity is too fast or the absorption is too slow, resulting in clinical pleural effusion. Preventive measures: 1. Active prevention and treatment of primary diseases. Pleural effusion is a part of chest or systemic disorders, so active prevention and treatment of primary diseases is the key to prevent this disease. 2.Enhance physical fitness and improve the ability to resist disease. Actively participate in a variety of suitable physical exercise, such as taijiquan, taiji sword, qigong, etc., to enhance physical fitness and improve the ability to resist disease. 3, pay attention to life conditioning. Keep your place of residence dry, avoid the invasion of dampness, do not eat cold, do not overeat, and keep the normal function of the spleen and stomach. After getting sick, timely treatment, avoid wind and cold, careful living, and pleasant mood, in order to achieve early recovery.