Headaches on the left side of the head may be caused by physiological reasons, such as excessive mental stress. It may also be caused by pathologic reasons, such as migraine, inferotemporal arteritis, etc., and the cause should be identified in a timely manner. 1. Physiological causes: left-sided headache may occur if there is too much mental stress or high mental tension. 2. Pathological causes (1) Migraine: Migraine is one of the common causes of headache on one side, which is an episodic headache caused by vascular dysfunction. (2) Temporal arteritis: Due to inflammation, the temporal artery near the temple becomes inflamed, which in turn causes vasculitis, leading to the symptoms of left-sided headache. If physiological causes are ruled out, one should consult a doctor in time to clarify the specific cause and, if necessary, carry out appropriate treatment.