Lower back pain affected 619 million people globally in 2020 and is the single leading cause of disability worldwide. The causes range from a simple muscle strain that heals in days to conditions involving your spine, nerves, or internal organs. Most cases trace back to something mechanical, meaning the muscles, ligaments, or bones in your lower back are under stress they can’t handle well. But some causes are less obvious and worth knowing about.
Muscle Strains and Ligament Sprains
The most common reason your lower back hurts is a strain or sprain of the soft tissue. A strain affects the muscles, while a sprain involves the ligaments that connect your vertebrae. Both feel similar: sudden pain in the lower back, muscle spasms that make the pain worse, and tenderness when you press on the area. These injuries happen during sports that involve pushing, pulling, or sudden twisting (think basketball, golf, tennis, or weightlifting), but they also happen from something as mundane as bending awkwardly to pick up a box.
Most muscle strains improve noticeably within a week. If pain isn’t decreasing after seven days, or if it’s getting worse rather than better, that’s a signal something else may be going on. Gentle movement generally helps recovery more than strict bed rest.
Disc Problems
Between each pair of vertebrae sits a rubbery disc that absorbs shock. These discs can cause pain in a few different ways, and the distinctions matter.
In degenerative disc disease, the discs gradually lose water content and their ability to handle pressure. They flatten, bulge, and lose height over time. This process can start surprisingly early. About 20% of young people already show mild signs of disc degeneration during adolescence. By age 50, roughly 10% of men are affected, and by 70, that number climbs to 50%. The pain tends to be a chronic, achy stiffness rather than a sharp, sudden event.
A herniated disc is more dramatic. It happens when the tough outer ring of the disc partially or fully ruptures, allowing the softer inner material to push outward into the spinal canal. This usually requires some degree of prior degeneration to occur, even if the triggering moment feels sudden, like lifting something heavy. When herniated material presses on a nearby nerve, the pain can radiate down into your leg.
Nerve Compression and Sciatica
When a disc, bone spur, or narrowed spinal canal presses on a nerve root, the pain often travels well beyond your lower back. Sciatica is the most recognizable version of this: a shooting or burning pain that runs from your lower back through your buttock and down one leg. Numbness, tingling, or weakness in the leg can accompany it.
Spinal stenosis is a narrowing of the spinal canal itself, which squeezes the nerves inside. The hallmark symptom is leg pain that gets worse when you walk and eases when you sit down or lean forward (like leaning on a shopping cart). If the narrowing happens in the center of the canal, symptoms can affect both legs. If it’s off to one side, you’ll typically feel it on that side only. Numbness and tingling from stenosis tend to involve the entire leg rather than a single isolated spot.
Inflammatory Back Pain
Not all lower back pain comes from physical injury. Inflammatory conditions like ankylosing spondylitis affect the joints where your spine meets your pelvis and can cause deep, persistent low back stiffness. Inflammatory back pain has a distinctive pattern that sets it apart from mechanical pain. It typically starts before age 40, comes on gradually rather than after a specific injury, improves with exercise, does not improve with rest, and wakes you up at night but feels better once you get moving in the morning. If four or five of those features describe your pain, an inflammatory condition is worth investigating.
Organ-Related Causes
Your lower back sits close to several organs, and problems in those organs can produce pain that feels like it’s coming from your spine even though it isn’t.
Kidney stones and kidney infections are classic examples. The pain usually sits to one side, just below your ribs toward the back, and may come with fever, painful urination, or blood in your urine. Unlike muscular back pain, kidney pain doesn’t change much with movement or position.
In women, endometriosis can cause lower back and pelvic pain that often worsens around menstruation. The tricky part is that endometriosis doesn’t always follow the textbook. Some people experience the expected period-related pain and pain during sex, while others have only urinary symptoms like frequent or painful urination, mimicking a bladder infection. When endometriotic tissue involves the ureters (the tubes connecting kidneys to the bladder), the vague symptoms can delay diagnosis and potentially affect kidney function over time.
Skeletal Irregularities
Scoliosis, an abnormal sideways curve of the spine, is most often detected in childhood or adolescence. Mild curves rarely cause pain, but larger curves that go untreated are more likely to lead to chronic back pain in adulthood. Spondylolisthesis, where one vertebra slips forward over the one below it, can cause a deep ache in the lower back along with stiffness and, if the slip is significant enough, nerve compression symptoms similar to stenosis.
Workplace and Lifestyle Risk Factors
Your daily habits play a larger role than most people realize. A large study of workers across key industries identified the factors most strongly linked to developing lower back pain. Repetitive trunk movements topped the list, increasing the odds by 57%. Working in the same posture at a high pace raised risk by about 40%. Regularly lifting loads over 20 kg (roughly 44 pounds) increased it by about 17%, and frequent overtime added another 19%.
Higher BMI, smoking, and regular use of vibrating tools at work also contributed. On the protective side, regular physical exercise reduced risk by about 12%, and having adequate rest time during the workday cut it by over 40%. Simply standing periodically rather than staying seated all day was also protective. The takeaway is that both too much physical strain and too little movement can set the stage for lower back pain.
When Lower Back Pain Is an Emergency
Most lower back pain, even when severe, is not dangerous. But a rare condition called cauda equina syndrome requires immediate emergency care. It happens when the bundle of nerves at the base of your spinal cord becomes severely compressed, usually by a large disc herniation. The warning signs are numbness in your groin or inner thighs (sometimes called “saddle” numbness because it affects the area that would contact a saddle), sudden loss of bladder or bowel control, and rapidly worsening weakness in one or both legs. These symptoms together represent a surgical emergency because delayed treatment can lead to permanent nerve damage.
Outside of that scenario, back pain that comes with unexplained weight loss, fever, or pain that wakes you from sleep and steadily worsens over weeks rather than improving deserves prompt medical evaluation, as these patterns can point to infection, inflammatory disease, or other conditions that benefit from early treatment.