Pleural effusion can cause coughing. In fact, in most patients with early pleural effusion, the main manifestation is a dry cough with no sputum or only a small amount of white foamy sputum. All parts of the human body, except the nails and hair, have a nerve distribution. Like the fingers, the nerve distribution is mainly used to sense touch, temperature and pain. However, the nerves in the lungs are very sensitive to the tensor reflex, which is the reflex of expansion and contraction of the lungs. Therefore, in patients with pleural effusion, the lungs are not fully dilated and expanded due to the pressure of the pleural effusion. In the early stage, because there is only a small amount of pleural effusion, the patient’s lungs are not obviously compressed, so there may not be obvious symptoms of dyspnea and chest tightness, but the compression of pleural effusion will cause part of the lungs to not be able to expand adequately. Moreover, when the patient changes position, such as after lying down or after changing from lying position to sitting up or standing up, the water flows to the lower part of the lung, and the pleural effusion will gradually change its position, such as from lying position with water on the back to sitting up position with water flowing to the diaphragm or bottom, at which time the lung originally compressed by the pleural effusion will gradually expand, while the lung later compressed by the pleural effusion will gradually shrink down, and Such an expanding or shrinking reflex will then stimulate the lungs, causing the person to feel a dry, itchy throat, resulting in a cough.