Lower back pain has a long list of possible causes, ranging from a simple muscle pull to conditions affecting the spine, organs, or even mental health. In 2020, it affected 619 million people globally, and most people will experience it at least once in their lives. Understanding what’s behind your pain is the first step toward knowing what to do about it.
Muscle Strains and Ligament Sprains
The most common cause of lower back pain is soft tissue injury. A strain happens when you overstretch or tear a muscle or tendon, while a sprain involves the ligaments that connect your vertebrae. Both can feel remarkably similar: a dull ache, stiffness, or sharp pain that worsens with movement.
These injuries typically happen during everyday activities done with poor form. Lifting something heavy without bending your knees, twisting while carrying a load, or even curving your lower back excessively while sitting can be enough to trigger one. Sports that involve pushing and pulling, like weightlifting and football, also increase the risk. A single awkward movement can do it, or the damage can build gradually from repeated overstressing of the back muscles. Most soft tissue injuries heal within a few weeks with rest and gentle movement, though they can be surprisingly painful in the meantime.
Disc Problems
Between each vertebra in your spine sits a disc that acts as a cushion. These discs have a tough outer layer and a softer interior, and problems with them are a frequent source of lower back pain.
A bulging disc occurs when the outer layer pushes outward, affecting a quarter to half of the disc’s circumference. The inner material stays contained, and many bulging discs cause no symptoms at all. A herniated disc is different: a crack in the outer layer allows some of the softer inner material to push through. Despite the common name “slipped disc,” the whole disc doesn’t actually move. Only the small area around the crack is affected.
Herniated discs are more likely to cause pain than bulging discs because the protruding material can irritate nearby nerve roots. More often than direct pressure, this irritation triggers inflammation around the nerve, which is what produces that sharp, radiating pain many people describe shooting down the leg. This nerve pain, sometimes called sciatica, can extend from the lower back through the buttock and all the way to the foot.
Spinal Stenosis
Spinal stenosis is a narrowing of the spaces inside your spinal canal, the tunnel running through your vertebrae that houses your spinal cord. When that space shrinks, it can compress or pinch the spinal cord and the nerves branching off it. This narrowing typically develops gradually, often from age-related changes like thickened ligaments, bone spurs, or bulging discs.
In the lower back, stenosis tends to cause pain that begins in the buttocks and extends down the leg, sometimes reaching the foot. Numbness, tingling, and weakness in the legs are also common. Many people with lumbar stenosis notice their symptoms worsen when standing or walking and improve when sitting or leaning forward, because bending slightly opens up the spinal canal.
Vertebral Slippage
Spondylolisthesis occurs when one vertebra slides forward over the one below it. This puts pressure on the surrounding structures and can pinch nerves. It’s graded on a scale from I to IV based on how far the bone has moved. Most cases, in both teens and adults, are low-grade (Grade I or II) and can be managed without surgery. High-grade cases (Grade III or IV) are much more likely to need surgical correction, especially when pain is severe or nerve function is affected.
In younger people, this condition often results from a stress fracture in the vertebra, sometimes from repetitive hyperextension in sports like gymnastics. In older adults, it more commonly develops from degenerative wear on the joints and discs that normally keep vertebrae locked in place.
Inflammatory Back Pain
Not all lower back pain comes from mechanical wear or injury. Inflammatory conditions like ankylosing spondylitis affect the joints at the base of the spine and can cause chronic pain that behaves very differently from a pulled muscle or disc problem.
The key differences are distinctive enough that doctors use them as screening criteria. Inflammatory back pain typically starts before age 35 and comes on gradually rather than after a specific injury. It persists for more than three months. The pain and stiffness are worst after periods of inactivity, particularly at night and first thing in the morning, and they actually improve with exercise and movement. This is essentially the opposite of mechanical back pain, which tends to feel worse with activity and better with rest. Anti-inflammatory medications like ibuprofen are highly effective for most people with inflammatory back pain, which can itself be a diagnostic clue.
Organ-Related Causes
Sometimes lower back pain has nothing to do with the spine at all. Several organs can produce pain that feels like it’s coming from the back.
Kidney stones are a well-known example, though the pain they cause is often mislocated by patients. Kidney stone pain typically hits in the flank, the area just below the ribs, not down near the waistline or buttocks. It often wraps around the side toward the pelvis or groin. When a stone moves closer to the bladder, it can also cause pain in the lower abdomen. If your back pain shoots down into the buttock or leg, a kidney stone is far less likely to be the cause.
Other organ-related sources include endometriosis, which can cause cyclical lower back pain tied to the menstrual cycle, and infections of the kidneys or urinary tract. Abdominal aortic aneurysms, though rare, can also present as deep, constant back pain.
Psychological and Social Factors
One of the most underappreciated causes of lasting lower back pain involves what’s happening in your life, not just your spine. Research has identified several psychological and social factors that increase the risk of acute back pain becoming a chronic problem.
Fear avoidance, the tendency to stop moving because you’re afraid of making the pain worse, is one of the strongest predictors. People who avoid activity after a back injury are roughly twice as likely to develop chronic pain compared to those who gradually return to movement. Lower socioeconomic status doubles the risk as well. Smoking increases it by about 24%. Poor social support networks, low mood, job dissatisfaction, and high stress levels all play a role. The severity of the initial pain matters too: people with high levels of pain at the outset are more than five times as likely to transition to chronic pain.
None of this means the pain isn’t real. It means that the brain’s pain processing systems are influenced by context, and addressing these factors alongside physical treatment leads to better outcomes.
When Back Pain Is an Emergency
Rarely, lower back pain signals a condition called cauda equina syndrome, where compressed nerve roots at the bottom of the spinal cord lose function rapidly. This is a true medical emergency that requires surgery within 24 to 48 hours to prevent permanent damage.
The warning signs are specific: lower back pain combined with numbness or tingling in the inner thighs, buttocks, or groin (sometimes called “saddle” numbness because it affects the area that would contact a saddle). Loss of bladder or bowel control, whether that means inability to go or inability to stop, is the most critical red flag. Sudden weakness in one or both legs alongside these symptoms warrants an immediate trip to the emergency room. These symptoms together are rare, but recognizing them quickly makes a significant difference in recovery.