Lower back pain affects 619 million people worldwide, and most people will experience it at least once in their lives. The causes range from a simple muscle strain that heals in days to chronic conditions that need ongoing management. Understanding what’s behind your pain helps you figure out whether it needs attention now, later, or not at all.
Muscle Strains and Ligament Sprains
Strains and sprains are the most common causes of lower back pain. You can injure the muscles, tendons, or ligaments in your lower back by lifting something too heavy, lifting with poor form, or twisting awkwardly. Some people strain their back doing something as minor as sneezing, coughing, or bending over to tie a shoe. The pain usually comes on suddenly, feels sharp or achy, and tends to worsen with movement.
These injuries typically heal on their own within a few days to a few weeks. Staying gently active tends to produce better outcomes than strict bed rest. If the pain hasn’t improved after about six weeks of basic self-care and gradual return to movement, that’s generally the point where further evaluation becomes worthwhile.
Disc Problems
The rubbery discs between your vertebrae act as shock absorbers. When one bulges out of position or tears (a herniated disc), it can press directly on a nearby nerve, sending sharp or shooting pain down into your buttock or leg. This nerve-related pain is often called sciatica. Large herniations can compress the bundle of nerves at the base of the spine, which is a more serious situation covered below.
As you age, discs naturally lose water content and flatten out, offering less cushioning between the bones. This process, called degenerative disc disease, is extremely common on imaging even in people with no symptoms at all. It can cause a dull, persistent ache in the lower back that worsens with prolonged sitting or bending forward. The name sounds alarming, but it’s a normal part of aging rather than a progressive disease in most cases.
Spinal Stenosis
Spinal stenosis is a narrowing of the spinal canal that puts pressure on the nerves running through it. It develops gradually, usually from a combination of thickened ligaments, enlarged joints, bone spurs, and flattened discs. It’s most common in people over 50.
The hallmark symptom is pain, heaviness, or cramping in the legs and buttocks that gets worse when you walk or stand and improves when you sit down or lean forward (like pushing a shopping cart). This happens because standing and walking slightly narrow the spinal canal further, reducing blood flow to the compressed nerves. Leaning forward opens the canal back up and relieves the pressure. If your lower back pain follows this pattern, stenosis is a likely contributor.
Inflammatory Back Pain
Not all lower back pain is mechanical. A group of conditions called axial spondyloarthritis causes inflammation in the joints and ligaments of the spine itself. This type of back pain behaves differently from a strain or disc problem in several distinct ways: it typically starts before age 45 (sometimes in the teens or twenties), lasts three months or longer, feels worse at night or after rest, improves with movement and exercise, and comes with notable morning stiffness.
If your back pain gets better when you move around and worse when you’re still, especially if you’re under 45 with no clear injury, inflammatory back pain is worth raising with your doctor. It’s often missed for years because it gets lumped in with generic “back pain,” but it responds to different treatments than mechanical causes do.
Weight, Sitting, and Other Risk Factors
Carrying extra weight puts meaningful stress on the lower back. People who are overweight have roughly 41% higher odds of developing chronic lower back pain compared to those at a normal weight, and people with obesity have about 48% higher odds. Prolonged sitting amplifies the effect. A large study using national health data found that sitting more than 4.5 hours a day acted as a multiplier: in people who sat that long, rising body weight was more strongly linked to chronic back pain than in people who sat less. Sedentary behavior was associated with higher risk of back pain in both work and non-work settings.
Smoking also appears in the risk profile. People with chronic lower back pain tend to have higher nicotine levels than those without it. The connection likely involves reduced blood flow to spinal structures and slower tissue healing. Physically demanding jobs that involve repetitive lifting, bending, or vibration (like operating heavy machinery) are well-established risk factors too.
Referred Pain From Other Organs
Sometimes lower back pain doesn’t come from the back at all. Kidney stones can cause pain that starts in the flank (the area just below the ribs on either side of the spine) and wraps around toward the lower abdomen or groin as the stone moves. In women, this pain can extend down to the pelvic area and feel like a menstrual cramp. However, kidney stones don’t typically cause pain that shoots into the buttock or leg, which is a useful way to distinguish them from spinal problems.
Other organs can refer pain to the lower back as well. Kidney infections, endometriosis, ovarian cysts, and certain abdominal conditions can all produce lower back discomfort. If your back pain comes with fever, painful urination, pelvic symptoms, or doesn’t change with movement or position, a non-spinal cause is more likely.
When Imaging Is Actually Needed
Most people with new lower back pain do not need an MRI or CT scan right away. Guidelines from the American College of Radiology are clear: uncomplicated lower back pain, even with leg symptoms, is typically a self-limiting condition that doesn’t warrant imaging. Scans frequently reveal “abnormalities” like bulging discs or mild degeneration that are present in pain-free people and can lead to unnecessary worry or procedures.
Imaging becomes appropriate in two situations. First, if your pain hasn’t improved after about six weeks of active management (staying mobile, physical therapy, basic pain relief). Second, if you have any red flags that suggest something more serious: a history of cancer, unexplained weight loss, recent significant trauma, prolonged steroid use, fever with back pain, or intravenous drug use. In these cases, an MRI without contrast is the standard first imaging choice.
Symptoms That Need Emergency Care
One rare but serious cause of lower back pain is cauda equina syndrome, where the bundle of nerves at the base of the spine becomes severely compressed. This can happen from a large disc herniation, spinal fracture, tumor, or infection. It requires emergency surgery to prevent permanent damage.
The warning signs are specific and hard to miss:
- Sudden difficulty urinating or inability to control your bladder
- Loss of bowel control or inability to feel when you need to go
- Numbness in the “saddle” area (inner thighs, buttocks, and groin)
- Progressive weakness in both legs
- Severe or rapidly worsening lower back pain alongside any of the above
Any combination of these symptoms with lower back pain warrants an immediate trip to the emergency room. Cauda equina syndrome is uncommon, but outcomes depend heavily on how quickly the pressure on the nerves is relieved.