Lower left back pain is most often caused by a strained muscle or ligament, but the left side specificity matters because several organs sit on that side of your body, including the left kidney, part of the colon, and (in women) the left ovary. Sorting out whether your pain is coming from your spine, your muscles, or an internal organ is the key question, and the type of pain you’re feeling usually points in the right direction.
Muscle Strain: The Most Common Cause
The most likely explanation for lower left back pain is a soft tissue injury. A strain means a muscle or tendon has been overstretched or torn, while a sprain involves a ligament. Both can happen on one side if you twisted, lifted something awkwardly, or simply overloaded the muscles during exercise or yard work.
One muscle that deserves special attention is the quadratus lumborum, a deep muscle that runs along each side of your lower spine. When this muscle is irritated, it causes a deep ache in the lower back that can also radiate into the hip or pelvis on the same side. It can feel sharp when you cough or sneeze. Common triggers include prolonged sitting or standing in one position, a sedentary lifestyle, poor posture, repetitive lifting, and pregnancy. Overuse is the most frequent cause, but weakness in the surrounding back muscles can also overload it, creating chronic pain with tight, tender knots called trigger points.
Muscle-related pain typically worsens with certain movements and eases with rest or a change in position. That positional quality is one of the clearest signs your pain is musculoskeletal rather than organ-related.
When a Nerve Is Involved
If your lower left back pain travels down into your buttock or leg, a nerve is likely being compressed. The most common scenario is a herniated disc in the lumbar spine pressing on a nerve root. The pain follows one of three typical patterns: it stays in the lower back, it extends into the buttock, or it radiates all the way down the leg. That traveling pain is often described as sharp, shooting, or electric, and it may come with numbness or tingling.
Facet joint problems can also cause one-sided back pain. These are the small joints that connect your vertebrae, and when they’re irritated, the pain tends to stay on one side and may spread into the buttock, occasionally mimicking the nerve pain of a herniated disc. The difference is that facet pain rarely travels below the knee.
Kidney Problems on the Left Side
Your left kidney sits in the upper-left part of your lower back, just below the ribs. Kidney stones and kidney infections are two of the most common organ-related causes of left-sided back pain, and both feel quite different from a muscle strain.
Kidney stone pain is serious and sharp, located in the side and back below the ribs, and it often radiates downward toward the lower abdomen and groin. It comes in waves, intensifying and then easing. Kidney infections tend to produce a constant, deep ache with tenderness when you press on the area just below the ribs on the affected side. Both conditions usually come with urinary symptoms: burning during urination, frequent urges to urinate, pink or red urine, cloudy or foul-smelling urine, or urinating in unusually small amounts. Fever and chills point more toward infection.
The key distinction is that kidney pain doesn’t change much when you shift positions. If lying down, standing up, or bending makes no difference to the pain, that’s a signal the source may not be your spine or muscles.
Digestive Causes
The lower portion of your colon, specifically the descending and sigmoid colon, runs along the left side of your abdomen and sits close to the back. Conditions affecting this part of the colon can refer pain to the lower left back.
Diverticulitis, where small pouches in the colon wall become inflamed or infected, is one of the more common examples. It typically causes lower left abdominal pain, but because the colon sits so close to the back, the pain can feel like it’s coming from behind. Complications like abscesses, bowel obstructions, or narrowing of the intestine can intensify back pain. Up to 50% of people with diverticulitis also develop constipation, which itself can cause or worsen back discomfort. You’ll usually have digestive symptoms alongside the back pain: bloating, changes in bowel habits, nausea, or abdominal tenderness.
Gynecological Conditions
In women, lower left back pain can originate from the reproductive organs. Endometriosis is one of the most common causes of non-spinal lower back pain. It occurs when tissue similar to the uterine lining grows outside the uterus, and it can produce pelvic pain that radiates into the back and even down the leg, mimicking a spinal problem. Ovarian endometriomas, sometimes called chocolate cysts, are cysts filled with old blood that develop on the ovary as a sign of endometriosis. These can cause back pain alongside painful periods, pain during intercourse, and sometimes anemia from chronic blood loss.
Pelvic inflammatory disease, an infection of the reproductive organs, can also cause lower back pain along with pelvic and abdominal pain, abnormal vaginal bleeding, and pain during sex. For men, prostatitis can produce pelvic pain that extends to the lower back, accompanied by urinary symptoms and sometimes signs of infection.
How Most Lower Back Pain Resolves
If your pain is musculoskeletal, the outlook is good. A large meta-analysis of back pain studies found that people with acute low back pain started at an average pain level of 52 out of 100, dropped to 23 by six weeks, and reached 12 by six months. The most dramatic improvement happens in those first six weeks, after which progress slows but continues. By one year, average pain scores dropped to 6 out of 100.
The often-cited statistic that 90% of acute back pain resolves within six weeks is somewhat optimistic. Well-conducted studies place short-term recovery rates between 39% and 76%, depending on how recovery is defined. Still, the overall trajectory is strongly toward improvement, and the vast majority of musculoskeletal back pain resolves without surgery or invasive procedures. Staying gently active, rather than resting in bed, tends to speed things along.
When Imaging Is Needed
For straightforward lower back pain without alarming symptoms, imaging like MRI or CT scans isn’t recommended right away. Current guidelines from the American College of Radiology consider uncomplicated acute back pain a self-limiting condition that doesn’t warrant imaging studies. The threshold for imaging is six weeks of conservative treatment (movement, physical therapy, pain management) without meaningful improvement, or the presence of red flags suggesting something more serious.
If imaging is eventually needed, MRI is the preferred first choice because it shows soft tissues like discs, nerves, and the spinal canal in detail. CT scans are better for evaluating bone, hardware from prior surgery, or when MRI isn’t available.
Red Flags That Need Prompt Attention
Most lower left back pain is not dangerous, but certain symptoms signal that something more serious may be happening. Seek medical care promptly if you experience any of the following alongside your back pain:
- Loss of bladder or bowel control, or numbness in the groin and inner thighs. This pattern suggests pressure on the bundle of nerves at the base of the spine, which requires urgent evaluation.
- Severe or worsening weakness in one or both legs, or rapidly progressing numbness.
- Fever, chills, or unexplained weight loss, which may indicate infection or another systemic cause.
- Pain that worsens at night or when lying flat, particularly if you have a history of cancer or immune suppression.
- Back pain following significant trauma, or even minor trauma if you’re older or have osteoporosis.
These red flags don’t necessarily mean something catastrophic is happening, but they do change the urgency. In these situations, imaging and further evaluation are warranted immediately rather than after weeks of conservative treatment.