What Makes Your Back Hurt? Common Causes Explained

Back pain stems from a surprisingly wide range of structures and processes, not just the spine itself. Muscles, discs, joints, nerves, and even organs elsewhere in the body can all produce pain that you feel in your back. What makes it tricky is that the same imaging finding can show up in someone with crippling pain and someone who feels perfectly fine, and psychological factors can genuinely amplify or perpetuate the physical experience. Understanding what actually generates back pain, and what doesn’t, can save you from unnecessary worry and steer you toward treatments that address the real problem.

Discs, Joints, and the Spine’s Load-Bearing Architecture

Your lumbar spine carries an enormous amount of force. During ordinary daily activities, the compressive loads on your lower vertebrae are already substantial, but sport-related movements like jumping and landing can push estimated compression at the L4/L5 level to more than ten times your body weight.¹ That load gets distributed across intervertebral discs, the small facet joints at the back of each vertebra, ligaments, and the muscles that wrap around the spine. When any of these structures is injured, inflamed, or degraded, pain follows.

The intervertebral discs act as shock absorbers between vertebrae, and their ability to do that job depends heavily on molecules called proteoglycans. These large molecules attract and hold water, giving the disc its cushion-like resilience. When proteoglycans are lost or damaged, the disc dries out, loses height, and becomes less effective at absorbing mechanical loads.² This process, disc degeneration, is one of the single most important risk factors for low back pain. A twin study of women in the UK found that individuals with advanced disc degeneration had roughly three times the odds of experiencing low back pain compared to those with minimal degeneration.³

The facet joints, meanwhile, are a frequently overlooked source of pain. These small paired joints guide spinal movement and bear a share of the spine’s compressive load. Facet joint pain accounts for roughly a quarter to two-fifths of low back pain cases, yet it is often misdiagnosed because there is no reliable correlation between what shows up on imaging, what the physical exam reveals, and how the patient actually feels.⁴ Facet joint pain tends to be worst with extension and twisting movements, but without a diagnostic nerve block, it can be hard to confirm.

Why a Herniated Disc Hurts More Than Simple Pressure Would Explain

For decades, the standard explanation for sciatica was straightforward: a herniated disc presses on a nerve root, and the pressure causes pain radiating down the leg. That explanation turns out to be incomplete. Several clinical observations don’t fit the pure-compression theory: disc surgery doesn’t always relieve pain, large herniations are sometimes painless, severe leg pain can exist without imaging evidence of nerve compression, and conservative treatment often works even when imaging looks alarming.⁵

The missing piece is inflammation. When disc material herniates, it doesn’t just sit there inertly squashing things. The herniated tissue is biologically active, releasing inflammatory mediators including interleukin-1, interleukin-6, and tumor necrosis factor.⁶ These chemicals irritate nearby nerve roots, sensitize pain receptors, and can trigger an autoimmune reaction in which the body attacks its own disc material. Researchers have identified a whole cascade of inflammatory agents, including phospholipase A2, prostaglandins, and immunoglobulins, in herniated disc tissue.⁷ This chemical irritation explains why small herniations can produce severe pain while large ones sometimes cause none at all. It also explains why anti-inflammatory treatments and time often resolve sciatica without surgery: the inflammation eventually calms down even if the structural bulge remains.

The Imaging Paradox

One of the most counterintuitive facts about back pain is that what shows up on an MRI often has little to do with whether someone hurts. A landmark study in the New England Journal of Medicine scanned the lumbar spines of 98 people with no back pain whatsoever. Only about a third had completely normal discs at every level. Roughly half had at least one disc bulge, and about a quarter had a disc protrusion.⁸ A more recent systematic review of over 3,100 asymptomatic individuals confirmed this pattern and showed that it gets more pronounced with age: disc degeneration was present in about 37% of 20-year-olds but 96% of 80-year-olds, and disc bulges went from 30% at age 20 to 84% at age 80.⁹

The practical takeaway is important: if you get an MRI for back pain and the report lists disc bulges, degeneration, or protrusions, those findings may or may not be causing your symptoms. They might simply be age-appropriate wear and tear that would have shown up regardless of whether you had pain. This doesn’t mean imaging is useless, but it does mean that findings need to be interpreted in context, matched against your symptoms and physical exam, rather than treated as a definitive explanation.

How Sitting, Posture, and Body Weight Load Your Spine

Sitting gets a bad reputation for back pain, and there is some biomechanical basis for it. A systematic review and meta-analysis measuring pressure inside lumbar discs found that sitting creates significantly higher intradiscal pressure than standing.¹⁰ When you sit, the natural lumbar curve tends to flatten, shifting more of the compressive load onto the front of the disc and reducing the load shared by the facet joints and posterior ligaments. Slouching amplifies this effect. But it’s worth noting that simply sitting in a chair isn’t inherently dangerous; prolonged static posture in any position is the real issue, because it reduces blood flow to spinal tissues and leaves the same structures under sustained load without relief.

Body weight compounds these forces. A biomechanical modeling study found that as body weight increased from about 51 kg to 119 kg, compression at the lowest lumbar level jumped by roughly 80% to 147% during flexed postures without holding anything, and by about 46% to 52% during tasks that involved holding a load.¹¹ In people with obesity, the effect was even larger because the extra abdominal mass shifts the center of gravity forward, increasing the lever arm that the spine has to counteract. This helps explain why weight loss is one of the most consistently effective interventions for chronic low back pain: it directly reduces the mechanical demand on spinal structures every time you bend, lift, or even just stand up.

How muscles wrap around the spine also matters. Research on spinal loading has shown that when compression follows the natural curves of the spine (rather than hitting it as a straight downward force), the spine can bear more load with a greater margin of safety against both instability and tissue injury.¹² This suggests that the way your muscles activate during movement, whether they distribute force along the spine’s curves or concentrate it at one point, plays a real role in whether a given activity is protective or harmful.

Core Weakness and Spinal Instability

The deep muscles that run along and between your vertebrae, particularly the multifidus and the transversus abdominis, act like a built-in brace for the spine. When these muscles are weak or poorly coordinated, the spine loses fine-grained stability, and other structures have to pick up the slack. Chronic low back pain has been linked to decreased cross-sectional area of the lumbar multifidus, and exercises designed to restore neuromuscular control of these muscles are a standard part of rehabilitation.¹³

This isn’t just a concern for people who are sedentary. A biomechanical study of runners found that weakness in the deep core musculature led to abnormal spinal loading patterns and muscle strain, both of which are associated with increased low back pain risk.¹⁴ In other words, a runner with strong legs but a weak core may be setting up their spine for trouble with every stride. The relevance extends to anyone performing repetitive movements: if the deep stabilizers aren’t doing their job, the superficial muscles and passive structures absorb forces they weren’t designed to handle repeatedly.

Trigger points in the muscles around the lower back can also complicate the picture. In a study of patients with lumbosacral radiculopathy, roughly two-thirds had identifiable trigger points. Patients who received trigger point injections alongside standard treatment saw their pain scores drop substantially more than those who received standard treatment alone.¹⁵ This suggests that muscular sources of pain often coexist with, and amplify, nerve-related pain. Treating one without addressing the other can leave people stuck.

When Your Nervous System Turns Up the Volume

Some people with chronic low back pain have no clear structural explanation for the severity of what they feel. This isn’t imaginary; it reflects a real change in how the nervous system processes pain signals, a phenomenon called central sensitization. In this state, the spinal cord and brain amplify incoming signals, so stimuli that should be mildly uncomfortable, or even neutral, register as painful.

Research has identified a distinct subgroup of chronic low back pain patients who show signs of central sensitization. One study found that about 48% of chronic low back pain participants met criteria for central sensitization, and these individuals had widespread pain sensitivity, dysfunctional pain-inhibition pathways, and significantly more anxiety, depression, and catastrophizing thoughts than those without it.¹⁶ Another study found that people with acute low back pain who had both heightened sensory sensitivity and negative psychological states (depressive symptoms, poor sleep, catastrophizing) were the least likely to recover at six months.¹⁷

The fear-avoidance model offers a useful way to understand how this plays out in practice. Pain catastrophizing, where a person interprets their pain as a sign that something terrible is happening, can lead to avoidance of movement. That avoidance leads to deconditioning, which leads to more pain when movement is attempted, which reinforces the catastrophizing. The cycle feeds itself. Studies of both chronic low back pain and knee osteoarthritis have confirmed that fear-avoidance behavior contributes meaningfully to pain chronicity and disability.¹⁸ None of this means the pain is “in your head.” It means the nervous system has genuinely changed in a way that requires different treatment strategies, often including graded exercise, cognitive behavioral therapy, and sometimes medications targeting central pain pathways.

Inflammatory and Autoimmune Back Pain

Not all back pain comes from mechanical wear and tear. A subset of people, often younger adults, have back pain driven by autoimmune inflammation. Conditions in the spondyloarthritis family, which include ankylosing spondylitis and psoriatic arthritis, cause inflammation in the sacroiliac joints and spine. The hallmark features are pain that is worse at night and in the morning, improves with movement rather than rest, and is accompanied by prolonged morning stiffness. Research has shown that the presence of night pain and morning stiffness is significantly associated with bone marrow edema in the sacroiliac joints on MRI, a sign of active inflammation.¹⁹

If your back pain started before age 40, has lasted more than three months, came on gradually, and gets better when you move around but worse when you sit still, it is worth asking your doctor specifically about inflammatory back pain. The average delay to diagnosis for ankylosing spondylitis is still measured in years, partly because the early symptoms overlap so heavily with ordinary mechanical back pain. The distinction matters because inflammatory back pain responds to different treatments, including biologic medications that target the underlying immune dysfunction, rather than the physical therapy and ergonomic changes that help mechanical pain.

Vertebral Compression Fractures

In older adults, especially those with osteoporosis, back pain can result from a vertebral compression fracture, sometimes from something as minor as a cough or bending to pick up an object. These fractures are the most common complication of osteoporosis, with about 700,000 cases reported annually in the United States.²⁰ They typically cause sudden-onset pain concentrated in the midline of the spine, along with a loss in height and reduced mobility.²¹

The tricky part is that more than two-thirds of vertebral compression fractures are found incidentally on imaging done for other reasons, meaning many people have them without realizing it.²⁰ A person may attribute worsening back pain and gradual height loss to “just getting older” when in fact they’ve had one or more fractures. If you’re over 50 and experiencing new midline back pain, especially if you have risk factors for osteoporosis, a fracture should be on the list of possibilities.

Back Pain That Isn’t Coming from Your Back

Some of the most important causes of back pain have nothing to do with the spine. Organs in the abdomen and pelvis can refer pain to the back, and missing these causes can have serious consequences. Kidney stones and kidney infections classically produce flank and back pain. Pancreatitis often causes pain that radiates to the middle back. Endometriosis can cause deep, cyclical low back pain in women.

One particularly dangerous source of referred back pain is an abdominal aortic aneurysm. A case report described a patient who presented with low back pain but had no identifiable mechanism of injury, no aggravating or easing factors, and constant symptoms that didn’t change with position. Physical examination of the lumbar spine was unremarkable, but abdominal palpation revealed a strong pulsation over the midline. Imaging confirmed an aneurysm measuring up to 5.5 cm, large enough to require urgent attention.²² The warning signs that back pain may not be spinal include pain that is constant regardless of position, pain that is not reproducible with spinal movement, unexplained weight loss, and pain accompanied by abdominal or pelvic symptoms.

Sleep, Genetics, and Why Some People Are More Vulnerable

Poor sleep doesn’t just make existing back pain feel worse; it appears to independently increase the risk of developing chronic back pain. A large prospective study found that people who reported poor sleep quality over a span of roughly a decade had about 65% higher risk of chronic back pain and roughly double the risk of back-related disability compared to good sleepers.²³ Meeting physical activity guidelines blunted this effect somewhat but didn’t eliminate it. The relationship likely runs in both directions: poor sleep heightens pain sensitivity and reduces tissue repair, while pain disrupts sleep, creating another self-reinforcing cycle.

Genetics also play a larger role than most people realize. The UK Twin Spine Study found that having a monozygotic twin with low back pain was associated with roughly six times higher odds of having it yourself, compared to about twice the odds for a dizygotic twin. Genetic background, disc degeneration, and being overweight were the factors most strongly linked to low back pain, and there was a significant genetic overlap between disc degeneration and the experience of pain itself.³ This doesn’t mean back pain is predetermined, but it does mean that two people exposed to the same physical demands can have very different outcomes partly because of the discs and vertebrae they inherited.

The Evolutionary Trade-Off of Walking Upright

From a comparative anatomy perspective, back pain is partly a design problem. Human spines evolved from a structure built for four-legged locomotion, and the adaptations that allow us to walk upright come with trade-offs. The lumbar curve (lordosis) that lets us balance our torso over our pelvis also creates shear stresses on the lower vertebrae. Researchers reviewing the evolutionary history of the human spine have argued that many people are poorly adapted to bipedalism, leaving them susceptible to low back pain through excessive lordosis, high shear stresses on the lower lumbar vertebrae, and thin neural arches.²⁴ The same adaptations that increased spinal mobility and load-bearing capacity in our ancestors also increased susceptibility to both posterior element loading and disc herniation.

Pregnancy adds another layer to this vulnerability. The growing uterus shifts the center of gravity forward, and hormonal changes (particularly increased relaxin) loosen the ligaments around the pelvis and spine. These pelvic changes and loading alterations combine to make low back and pelvic pain extremely common in pregnancy.²⁵ The same ligament laxity that helps the pelvis accommodate delivery also reduces the passive stability of the lower spine, putting more demand on muscles that may already be stretched and weakened by the expanding abdomen. For most women, these symptoms resolve after delivery, but for a significant minority, they persist and can require targeted rehabilitation.

Spinal Stenosis and Aging

Lumbar spinal stenosis is a narrowing of the spinal canal that tends to develop gradually in people over 60. As discs lose height, facet joints enlarge, and ligaments thicken, the available space for the spinal nerves shrinks. The hallmark symptom isn’t ordinary back pain but neurogenic claudication: leg pain, heaviness, or numbness that comes on with walking and is relieved by sitting down or leaning forward, such as over a shopping cart. A randomized trial of patients with imaging-confirmed lumbar spinal stenosis found a mean age of about 71 years, with the majority having had leg symptoms for over a year and a mean maximum walking capacity of roughly 330 meters before symptoms forced them to stop.²⁶

What makes stenosis distinctive is the postural component. Leaning forward opens the spinal canal slightly, so people with stenosis often feel fine cycling or pushing a grocery cart but cannot walk the same distance standing upright. If you find that your legs give you trouble when you walk but feel fine when you sit or bend forward, stenosis is worth investigating, especially if you’re over 60.