Numbness of the left lateral thigh may be caused by lateral femoral dermal neuritis, pyriformis syndrome, lumbar disc herniation, lower extremity artery occlusion, etc. 1. Lateral femoral dermal neuritis: when the patient’s lateral thigh nerve is damaged, it leads to abnormal sensation in the skin area, resulting in numbness in the left lateral thigh, accompanied by pain and burning sensation. 2. Piriformis syndrome: numbness of the left lateral thigh may be caused by piriformis syndrome, which is usually caused by the sciatic nerve in the region of piriformis muscle compression, usually manifested as buttock pain and lower extremity radiating pain. 3. Herniated lumbar intervertebral discs: If the intervertebral discs are ruptured under long-term exertion and external force, the nucleus pulposus and annulus fibrosus will protrude backward, and in severe cases, the nerve is compressed, which leads to numbness of the left side of the lateral thigh. 4. Lower limb arterial occlusion: if the lower limb arterial atherosclerotic lesions, stenosis or occlusion, resulting in numbness of the outer thigh, accompanied by resting limb pain, intermittent claudication. It is recommended that patients go to the hospital in time, under the diagnosis of the doctor, according to the condition to take targeted treatment.