Pulmonary effusion, or medically known as pleural effusion. Various causes lead to excessive fluid in the chest cavity and the lungs are squeezed, producing symptoms such as chest tightness and difficulty in breathing. Chronic patients may have difficulty lying down and need to be semi-recumbent or sitting to be comfortable. If necessary, some of the chest fluid should be released to relieve the symptoms. Whether or not hydrocele is contagious depends on the cause of the disease, and most are not contagious. Pleural effusion has many etiologies. There are pneumonia, tuberculosis, cancer, hypoproteinemia due to various diseases, autoimmune diseases, bleeding from chest trauma, and heart failure. Among the above causes, tuberculosis disease, if the patient is in the active stage of tuberculosis, it is possible to transmit the tuberculosis bacillus to other people through the sputum or other secretions carried in the patient’s lungs when coughing. Therefore, if a patient has a pleural effusion, appropriate protective measures, such as wearing a mask, are required. Patients with pleural effusion due to other etiologies do not transmit the disease to others. Therefore, whether or not pleural effusion is contagious, the first thing to do is to find out the cause of the disease. Most of them are not contagious, but once pleural effusion occurs, it is recommended to go to a regular hospital as soon as possible and perform symptomatic supportive treatment while actively identifying the cause of the disease for more effective treatment. Otherwise, there may be more serious consequences.