Sciatica pain happens when something presses on or irritates the sciatic nerve, which runs from the lower back through the hips and buttocks and down each leg. The cause is almost always compression at or near the spine, though muscles and other soft tissues can sometimes be the culprit. Understanding what’s behind your specific pain matters because treatment depends entirely on the source.
Herniated Discs: The Most Common Cause
A herniated disc is responsible for more sciatica cases than any other single cause. The rubbery discs between your vertebrae act as shock absorbers, and when the soft inner material pushes through a tear in the tougher outer layer, it can press directly on a nearby nerve root. This is especially common in the lower spine: 95% of lumbar disc herniations occur at the L4-L5 or L5-S1 levels, which are the two lowest disc spaces and exactly where the nerve roots feeding the sciatic nerve exit the spine.
A herniated disc can happen suddenly from lifting something heavy with poor form, or it can develop gradually as discs lose water content and become less flexible with age. You might feel a sharp, shooting pain that travels from your lower back into your buttock and down the back of one leg. Coughing, sneezing, or sitting for long periods often makes it worse because these actions increase pressure inside the disc.
Spinal Stenosis
Spinal stenosis is a narrowing of the bony canal that houses your spinal cord and nerve roots. As the tunnel shrinks, it squeezes the nerves passing through it. The narrowing can happen in the main central channel or at the individual exit points where each nerve root branches off (called foraminal stenosis). Either type can compress the nerve roots that form the sciatic nerve.
This condition most commonly affects people between the ages of 50 and 60, and it’s usually driven by arthritis-related changes in the spine. Over time, bone spurs grow, ligaments thicken, and the joints enlarge, all of which eat into the available space for your nerves. Unlike a herniated disc, which can cause sudden sciatica, stenosis tends to creep up gradually. Walking and standing often make the pain worse, while sitting or leaning forward (which opens up the spinal canal slightly) brings relief.
A less common form, called developmental or congenital stenosis, affects people who were born with a naturally narrower spinal canal. These individuals can develop symptoms as early as their late teens or twenties, especially if even minor disc bulging or joint changes tip them over the threshold.
Spondylolisthesis
Spondylolisthesis occurs when one vertebra slips forward over the one below it. That slippage distorts the alignment of the spine and narrows the openings where nerve roots exit, putting direct pressure on the nerves. It can also stretch or kink the nerve root itself.
This condition has several causes. In younger people, it’s often related to a stress fracture in a part of the vertebra called the pars interarticularis, common in athletes who repeatedly extend their spines (gymnasts, football linemen). In older adults, it typically results from degenerative changes in the facet joints and discs that allow one vertebra to gradually slide out of position. The pain pattern usually includes both lower back pain and radiating leg pain, and it tends to worsen with standing and walking.
Piriformis Syndrome
Not all sciatica originates in the spine. The piriformis is a small muscle deep in the buttock that runs from the base of the spine to the top of the thigh bone. The sciatic nerve passes directly beneath it (and in some people, straight through it). When the piriformis muscle spasms, tightens, or swells from overuse or injury, it can compress the sciatic nerve and produce pain that feels identical to spine-related sciatica.
The key difference is location. Piriformis syndrome typically causes deep buttock pain that radiates down the back of the leg, but without the lower back pain that accompanies most disc or stenosis problems. Sitting for long periods, climbing stairs, and running tend to aggravate it. The condition is sometimes triggered by a fall onto the buttock, prolonged sitting on hard surfaces, or repetitive activities like long-distance running. Diagnosing it can be tricky because it doesn’t show up on standard spinal imaging, so doctors rely on physical exam maneuvers that stretch or activate the piriformis muscle to reproduce the pain.
Pregnancy-Related Sciatica
Sciatica during pregnancy results from a combination of hormonal shifts and mechanical changes. The hormone relaxin, which your body produces to loosen tendons and ligaments in preparation for delivery, also loosens the joints of the pelvis and lower spine. That added flexibility can allow subtle shifts in spinal alignment that irritate nerve roots.
At the same time, your growing belly pulls your center of gravity forward, increasing the curve of your lower back as your body tries to redistribute the weight. This exaggerated curve compresses the structures in the back of the spine where nerve roots exit. During the second and third trimesters, the baby’s position can compress the sciatic nerve even further. The combination of hormonal loosening, postural changes, and direct pressure from the fetus explains why sciatica is particularly common in late pregnancy, and why it usually resolves after delivery.
Other Structural Causes
Several additional conditions can compress or irritate the sciatic nerve roots. Bone spurs (osteophytes) that develop along the edges of vertebrae can jut into the space where nerve roots travel. Thickened ligaments inside the spinal canal, particularly the ligamentum flavum, can fold inward and narrow the available space. Cysts that form on the facet joints of the spine occasionally grow large enough to press on a nerve root.
Trauma from car accidents, falls, or sports injuries can cause fractures, dislocations, or swelling that compresses the nerve acutely. Scar tissue from a previous spinal surgery can also tether or compress nerve roots, a condition called epidural fibrosis. Even something as simple as prolonged sitting with a wallet in your back pocket has been associated with sciatic nerve irritation in the buttock.
Tumors and Infections
Rarely, sciatica is caused by a spinal tumor or infection rather than a mechanical problem. These cases account for a small percentage of all sciatica, but they require different and more urgent treatment. A tumor growing near the spinal canal can compress nerve roots in the same way a herniated disc does, producing leg pain, numbness, and weakness.
Certain features distinguish this kind of pain from the more common mechanical causes. Spinal tumor pain often gets worse at night or when lying flat, rather than improving with rest the way most disc-related pain does. Tumors can release chemicals that increase pain when the body is at rest. Other warning signs include pain that steadily worsens over weeks, unexplained weight loss, severe fatigue, and pain that doesn’t respond to over-the-counter medications. Back pain that you can’t explain, that lasts more than a few weeks, and that keeps getting worse deserves medical evaluation even if you don’t have all of these features.
Cauda Equina Syndrome: A True Emergency
Cauda equina syndrome happens when something (usually a massive disc herniation, but sometimes a tumor, infection, or fracture) compresses the bundle of nerve roots at the very bottom of the spinal cord. This is rare, but it requires emergency surgery to prevent permanent damage.
The hallmark symptoms go beyond typical sciatica. Watch for numbness or strange sensations (burning, tingling, prickling) in the backs of your legs, buttocks, hips, or inner thighs. Difficulty urinating or having a bowel movement, or the opposite problem of being unable to control your bladder or bowels, is the most critical red flag. Loss of the sensation that tells you when you need to use the bathroom, rapidly worsening leg weakness, or difficulty walking alongside lower back and leg pain all warrant an immediate emergency room visit. Hours matter with this condition, and delays in treatment can result in permanent loss of bladder and bowel function.
What Affects Recovery
The good news is that most sciatica improves without surgery. Approximately 60% of patients recover within six weeks with conservative care such as physical therapy, anti-inflammatory medications, and activity modification. Most cases of acute sciatica improve significantly within four to six weeks regardless of the specific cause.
Several factors influence how quickly you recover. Younger patients and those without significant nerve damage tend to bounce back faster. Sciatica caused by a disc herniation often resolves on its own as the herniated material shrinks over time and inflammation settles down. Stenosis-related sciatica, on the other hand, tends to be more chronic because the structural narrowing doesn’t reverse itself, though symptoms can often be managed long-term with exercise and postural strategies. Piriformis syndrome typically responds well to targeted stretching and physical therapy once correctly identified. The underlying cause shapes not just the timeline but also which treatments are most likely to help, which is why getting an accurate diagnosis matters more than simply treating the pain.