Numbness of the thighs may be caused by the following factors.1. If there is a recent long-term sitting or standing posture is not appropriate, compression of the thighs, so that the local blood circulation is not good, the phenomenon of numbness of the thighs will occur.2. Consider lumbar intervertebral disc herniation, the third lumbar vertebrae herniation syndrome and other diseases, if the lesion compresses the nerves, the radiating pain of the lower limbs, as well as the numbness of the sensation.3. Consider the auto-immune disease, for example, diabetes later affects the cerebral nerves can also occur. Immunological diseases, for example, diabetes mellitus in the late stage affects the brain nerves, this phenomenon can also occur.