Pulmonary effusion, also known as pleural effusion, is mainly caused by abnormalities in the pleura, and common causes include pneumonia, tuberculosis, lung cancer, heart failure, abnormal liver and kidney function, and trauma. 1. Pneumonia: Inflammatory lesions in the lungs will cause irritation to the pleura, which will further lead to localized exudation, causing pleural effusion. 2. Tuberculosis: tuberculosis in the lungs, if not controlled in time, can also lead to pleural irritation, especially tuberculous pleurisy, which can also lead to fluid exudation in the pleural cavity, resulting in effusion. 3. Lung cancer: tumors in the lungs can also cause irritation to the pleura, which may lead to abnormal reflux of capillaries and lymphatic vessels, causing fluid leakage and resulting in pleural effusion. 4. Abnormal liver and kidney function: abnormal liver and kidney function leads to hypoproteinemia, which causes plasma colloid osmotic pressure to decrease, and further leads to fluid leakage into the pleural cavity, resulting in effusion. 5. Trauma: Trauma can cause damage to the blood vessels and lymphatic vessels around the pleural cavity, leading to fluid directly entering the pleural cavity and causing effusion. When obvious pleural effusion occurs with symptoms such as chest tightness, shortness of breath and wheezing, it is necessary to consult a doctor in time and carry out standardized treatment under the guidance of a clinician.