Left side back back pain may be due to acute lumbar sprain, lumbar muscle strain, lumbar disc herniation and other causes. It may also be caused by non-disease reasons such as cold and excessive exercise. 1. Acute lumbar sprain: when the load borne by the lumbar region is large, it may cause damage to muscle fibers, congestion, edema and other phenomena occur. If the left side of the lumbar sprain to the injury, there will be a left side of the back of the back pain. 2. Lumbar muscle strain: due to long-term overload of the left lumbar muscles, involving the left lumbar muscles, lumbar muscle strain may occur, manifested in the left side of the back back pain, usually the left side of the lumbar muscles, periosteum, fascia will also be damaged inflammation, aggravating low back pain. 3. Lumbar intervertebral disc herniation: if long-term stooping to do heavy physical work, it may induce lumbar intervertebral disc herniation, if the lumbar intervertebral disc is biased to the left and right side, there will be a left-sided back back pain Patients should pay attention to keep warm in daily life and do not overload physical work or exercise. Related patients should seek timely medical examination and targeted treatment.