There are many reasons for the pain under the left rib sometimes and sometimes not, such as pleural effusion, intercostal neuritis, lung lesions and so on. 1. Pleural effusion: pleural effusion is mainly due to local inflammation, if it is not treated, it can cause the phenomenon of pain under the left rib sometimes and sometimes not. 2. Intercostal neuritis: Intercostal neuritis can also cause pain under the left rib sometimes and sometimes not, especially after overwork and cold. 3. Lung disease: lung infection, bronchitis, pleurisy, pneumothorax, lung cancer and other diseases can also cause pain and sometimes no pain under the left rib, and may be accompanied by coughing, dyspnea and other phenomena. There are many reasons for the pain under the left rib sometimes and sometimes not, after the emergence of symptoms, it is recommended to consult a doctor in time, take standardized treatment according to the doctor’s instructions, do not ignore the symptoms and take it lightly.