Numbness on the left side of the neck is mainly considered to be caused by cervical spondylosis; in addition, neck trauma, insufficient blood supply and skin allergy are also possible causes. Numbness on the left side of the neck is a common manifestation of cervical spondylosis, especially neurogenic cervical spondylosis, which is mainly due to cervical spondylotic hyperplasia or ligament thickening, disc herniation, etc., which compresses the sensory nerves in the neck. Patients may also experience stiffness and soreness in the neck. It mostly occurs in people who work at desk for a long period of time and lack of activity in the neck. If the neck is traumatized, which damages the sensory nerves in the neck, the symptoms of numbness may also be present. Numbness may also be manifested by impaired circulation and insufficient blood supply to the skin of the neck. Additionally, if the skin of the neck is sensitized, this may also cause numbness. This is often accompanied by redness and rashes on the skin of the neck. If the numbness on the left side of the neck persists or worsens progressively, it is recommended to go to the hospital in time to get a clear cause and reasonable treatment.