Left brain pain usually refers to headache on the left side, and the causes of pain are very complicated, mainly including: primary headache, left brain occupying lesion, intracranial infection, cerebral infarction and so on. 1. Primary headache: caused by migraine or tension headache, usually appearing after prolonged tension, frequent late night, poor rest, can be manifested as pain on one side of the brain or bilateral pain, which can be relieved by acupuncture or massage. 2. Occupying lesions on the left side of the brain: such as brain tumors and cysts. Occupational lesions can lead to local edema and increase intracranial pressure, which will lead to left headache, nausea, vomiting and other manifestations. 3. Intracranial infection: usually caused by viruses or purulent bacteria, such as encephalitis, meningitis and so on. Patients may also have left-sided headache, usually accompanied by fever, meningeal irritation and other symptoms. 4. Cerebral hemorrhage: Cerebral hemorrhage can cause edema of brain tissue, and the hemorrhage stimulates the meninges to cause left-sided headache, and there will be weakness, numbness, and incoordination of the right side of the limbs. 5. Other diseases: for example, high blood pressure, pulmonary encephalopathy, etc., may also appear in the left side of the headache phenomenon, usually accompanied by other uncomfortable symptoms. In conclusion, there are many causes of left side headache, it is recommended to go to the regular hospital in time, clear examination and symptomatic treatment.