Low back pain is the single leading cause of disability worldwide, affecting an estimated 619 million people in 2020 alone. Its causes range from simple muscle strains to serious underlying conditions, and understanding what’s behind your pain is the first step toward addressing it. Most cases trace back to something mechanical, meaning the pain originates in the spine, discs, or surrounding muscles. But organs, inflammatory diseases, and even psychological factors can all play a role.
Muscle Strains and Sprains
The most common reason for a sudden episode of low back pain is a strained muscle or sprained ligament. This usually follows either a single incident, like awkwardly lifting a heavy box, or repetitive overuse from work or exercise. The hallmark of this type of pain is that it gets worse with movement and eases up with rest. Workplace injuries are a particularly frequent trigger, especially in jobs that involve heavy lifting, bending, or prolonged awkward postures.
Most muscle strains resolve within a few weeks with basic self-care. The bigger concern is when that initial injury leads to guarding behaviors, where you start moving less and bracing constantly because you’re afraid of re-injury. That pattern can set the stage for pain that lingers far longer than the original strain would have on its own.
Disc Problems
Between each vertebra sits a cushioning disc with a tough outer shell and a softer interior. Over time, or after an injury, the outer shell can weaken and the inner material can bulge outward or rupture completely. This is called a herniated disc. When that bulging material presses against a nearby nerve, it can cause pain that radiates down one or both legs, a pattern commonly known as sciatica.
Disc herniations are most common in people between their 30s and 50s, when the discs are still hydrated enough to herniate rather than simply dry out. Many herniated discs actually cause no symptoms at all and are found incidentally on imaging. When they do cause pain, it tends to worsen with sitting, bending forward, or coughing.
Age-Related Wear and Tear
Most people over 50 have experienced low back pain, and much of it stems from cumulative changes in the spine. As you age, the soft discs between vertebrae dry out, lose height, and become less effective as shock absorbers. The joints connecting vertebrae develop arthritis, causing bones and ligaments to thicken. These changes are nearly universal and don’t always cause pain, but in many people they do.
One of the more significant consequences is spinal stenosis, a narrowing of the canal that houses the spinal cord and nerve roots. The most common cause of spinal stenosis is osteoarthritis. As the canal shrinks, it puts pressure on the nerves passing through it, often causing pain, weakness, or numbness in the legs. A classic pattern is leg pain that worsens with walking and improves when you sit down or lean forward, like over a shopping cart.
Inflammatory Conditions
Not all back pain is mechanical. Inflammatory conditions like ankylosing spondylitis produce a distinctly different pattern. The most common symptom is lower back and hip pain with stiffness, but the key difference is timing: inflammatory back pain typically worsens during rest or inactivity. People often notice it most in the middle of the night or after prolonged sitting. Movement and exercise tend to improve it, which is the opposite of what happens with a muscle strain.
Ankylosing spondylitis is part of a family of conditions called spondyloarthritis that can also involve the eyes, skin, and gut. Someone with inflammatory back pain might also develop eye inflammation (uveitis), psoriasis, or inflammatory bowel disease. If your back pain consistently improves with activity, started before age 40, and came on gradually rather than after an injury, an inflammatory cause is worth investigating.
Structural Spinal Curvatures
A healthy spine has a gentle S-shaped curve when viewed from the side, which distributes weight evenly and allows flexible movement. When that curvature becomes exaggerated or misaligned, it can shift how forces are distributed across the spine and its supporting muscles. Conditions like scoliosis (a sideways curve), excessive kyphosis (a rounded upper back), or excessive lordosis (an exaggerated inward curve in the lower back) can all contribute to chronic low back pain. In severe cases, kyphosis can cause not only pain but breathing difficulties from pressure on the lungs. Maintaining a healthy weight helps reduce the extra load these curvatures place on the spine.
Pain From Other Organs
Sometimes the source of low back pain isn’t the back at all. Internal organs can produce what’s called referred pain, where a problem in one area of the body is felt somewhere else entirely. Lower back pain or pain in the flank area can indicate kidney issues, such as kidney stones or an infection, or problems with the colon. Conditions affecting the upper abdomen, like gallstones or pancreatitis, more commonly refer pain to the upper back between the shoulder blades.
The key distinction is that organ-related back pain usually doesn’t change with spinal movement. Bending, twisting, or lying down won’t make it better or worse the way a muscle strain would. It may come with other symptoms like fever, changes in urination, or abdominal pain. If your back pain doesn’t seem connected to movement at all, the cause may not be your back.
Occupational and Lifestyle Risk Factors
Three modifiable risk factors consistently drive the global burden of low back pain: occupational ergonomic factors, smoking, and elevated body mass index. On the occupational side, the specific hazards include heavy lifting, difficult postures, repetitive motions, hand vibration, kneeling, squatting, and climbing. But desk work isn’t protective either. The shift toward sedentary work styles may paradoxically increase chronic low back pain by weakening the muscles that support the spine and keeping the body in sustained, static positions for hours.
Smoking contributes through reduced blood flow to spinal structures and impaired disc nutrition. Excess body weight increases the compressive load on the lumbar spine with every step. Both are factors you can change, and both meaningfully affect your risk.
How Psychology Shapes Chronic Pain
One of the less obvious causes of persistent low back pain is your brain’s response to it. Psychosocial risk factors, sometimes called “yellow flags,” include fear of movement, beliefs that back pain signals serious harm, low mood, social withdrawal, and an expectation that only passive treatments like massage or medication will help. People who focus heavily on their pain, feel anxious about it, and catastrophize about the worst possible outcome are at higher risk of their acute pain becoming chronic.
This doesn’t mean the pain isn’t real. It means the nervous system can amplify and sustain pain signals based on emotional and cognitive patterns. Fear-avoidance behavior is a common example: you hurt your back, become afraid of re-injury, stop moving, lose conditioning, and the pain persists or worsens. Breaking that cycle through gradual, guided return to activity is one of the most effective strategies for preventing short-term back pain from becoming a long-term problem.
Signs That Need Urgent Attention
The vast majority of low back pain is not dangerous, but a small number of cases involve conditions that require emergency care. Cauda equina syndrome occurs when the bundle of nerves at the base of the spinal cord becomes severely compressed, and it can cause permanent damage if not treated quickly. The most telling symptom is urinary retention, where your bladder fills but you don’t feel the normal urge to urinate. Other warning signs include loss of bowel or bladder control, numbness in the groin, inner thighs, or buttocks (called saddle numbness), progressive weakness in one or both legs, and sexual dysfunction.
Back pain accompanied by unexplained weight loss, fever, or a history of cancer also warrants prompt evaluation. These patterns are uncommon, but recognizing them matters because the window for effective treatment can be narrow.