Fluid in the lungs is not necessarily cancer. There are many causes of pulmonary effusion, and cancer is only one of the causes of pulmonary effusion. Pulmonary effusion is clinically known as pleural effusion, which mainly manifests as abnormal fluid accumulation in the chest cavity and can be divided into leaky pleural effusion and exudative pleural effusion. If it is a leaky pleural effusion, the etiology may be congestive heart failure, liver cirrhosis, etc. In the case of exudative pleural effusion, the etiology may be thoracic malignancy, tuberculosis, parasitic infection, systemic lupus erythematosus, lymphoma, liver abscess, uremia, hemothorax, multiple myeloma, endometriosis, etc. In addition, trauma such as rib fracture can also cause pneumothorax and lead to pleural effusion. Therefore, patients with pulmonary effusion need to undergo a detailed examination before a clear diagnosis can be made and targeted treatment can be administered. In daily life, patients with pulmonary effusion should avoid strenuous exercise, ensure regular work and rest, eat less spicy and stimulating food, and eat more protein-rich food to facilitate the treatment of the disease.