Hidden pain in the lower left side of the lower back is usually due to pathological factors, and the causes of lumbar pain may be lumbar disc herniation, lumbar muscle strain and lumbar dorsal myofasciitis, and urinary system diseases. 1. Lumbar disc herniation: If the lumbar disc annulus fibrosus ruptures and the nucleus pulposus presses on the nerve root, persistent low back pain usually occurs, which is generally tolerable. Therefore, lumbar disc herniation may be the cause of left lower back pain. 2. Lumbar muscle strain and myofasciitis of the lumbar back: it is a kind of chronic strain aseptic inflammation that occurs in the muscles or myofascia of the lumbar back, which may show hidden pain in the lower left side of the waist. 3. Urological diseases: pyelonephritis, perinephric abscess, kidney stone, kidney tumor and other diseases may cause increased tension on the membrane of the kidney, spasm of the ureter and renal pelvis, which may cause pain in the lower left side of the waist. Besides, trauma to the lower back and tumor occupation may also cause lower back pain. If the pain is difficult to be relieved on its own, it is recommended to consult a doctor and take appropriate treatment according to the cause of the pain.