Numbness on the left side of the head may be related to physiological factors, or may be caused by neurasthenia, cervical spondylosis, cerebral infarction and other reasons. 1. Physiological factors: if the head is biased to the left side for a long time during sleep, resulting in the left side of the head for a long time under pressure, resulting in poor blood circulation, it may cause numbness on the left side of the head. 2. Neurasthenia: the disease can lead to patients with combined sleep disorders, resulting in insufficient sleep, poor rest, may cause numbness on the left side of the head, may also be accompanied by forgetfulness, temper tantrums and other manifestations. 3. Cervical spondylosis: the protruding cervical intervertebral disc is easy to local blood vessels, nerve root compression, causing insufficient blood supply to the vertebral artery or compression of the occipital nerve, the left side of the scalp may be numbness, may be accompanied by neck and shoulder pain, hand numbness and other manifestations. 4. Cerebral infarction: due to local ischemia of brain tissue, resulting in damage to the cerebral nerves in the area, inducing cerebral dysfunction, which may cause numbness on the left side of the scalp, which may also be accompanied by speech disorders, swallowing disorders and other manifestations. Numbness on the left side of the head, exclude physiological factors, should consult a doctor in time, after clarifying the cause, give targeted treatment.