The left side of the back often numb, the specific reasons are as follows: First, the back of the local fasciitis: when long hours of ambulation, often bending labor, head down to play cell phones, when carrying heavy objects, can cause the back of the fascia pressure, tension increased. Over time, the fascia will produce a jamming of the dermal nerve in and out of the fascia, there will be a numbness of the skin on the surface of the fascia, and can be accompanied by localized soreness and pain. Second, spinal neurogenic diseases: such as thoracic spinal stenosis, when the thoracic medulla is compressed by the hyperplastic structures in the spinal canal, often manifesting as a sense of thoracic fasciculations, including, of course, numbness in the back and numbness in the forehead.