Numbness of the left big toe may be caused by a variety of reasons, such as peripheral neuritis, lumbar disc herniation, left pyriformis syndrome, peripheral neuropathy, arterial occlusive disease and so on. It is recommended to go to the hospital for examination to determine the specific cause. Common causes are as follows: 1. Peripheral neuritis: the symptom of numbness of the big toe, accompanied by redness, swelling, fever and localized pressure pain. 2. Lumbar intervertebral disc herniation: especially when the intervertebral disc of lumbar 5 sacral 1 is herniated, it can be manifested as numbness of the left thumb. The herniated disc can cause numbness of the left thumb when it compresses the nerves affecting the lower limbs. 3. Piriformis syndrome: the sciatic nerve is squeezed in the process of passing through the piriformis muscle in the buttocks, and the left piriformis syndrome occurs, causing damage to the nerves innervating the thumb, which manifests itself as numbness and weakness of the big toe that can’t be lifted. 4. Peripheral neuropathy: localized lesions of the nerves in the left foot or peripheral neuropathy such as neuritis can cause numbness in the big toe. 5. Arterial occlusion: Arterial occlusive disease of the left foot leads to ischemia and hypoxia of the local soft tissues, resulting in numbness of the left big toe and limitation of activities. There may be other reasons for the numbness of the left big toe, so it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, and then follow the doctor’s instructions for treatment.