Sitting up with no pain in the buttocks on the left side can be caused by a herniated disc in the lumbar spine, or it can be caused by sciatica. In addition, it may also be caused by physiological reasons. 1. If you are sedentary for a long period of time, the lack of blood circulation in the sciatic area may cause the above symptoms, which is a physiological cause. 2. Herniated lumbar disc: if you suffer from herniated lumbar disc and other diseases, and do not get timely and effective treatment, it will make the local nerves are subjected to a certain degree of compression, thus involving the sciatic nerve area, there will be the left side of the buttocks do not hurt to sit up the sciatic pain, which belongs to a pathological cause. 3. Sciatica: if the sciatic nerve area is damaged, there may be radioactive pain, so after the local compression, there may be left-sided lying buttocks do not hurt sitting up sciatic pain, which also belongs to a pathological cause. The phenomenon, you need to consult a doctor in time to avoid leaving a future problem.