Sciatic nerve pain usually comes from something pressing on or irritating the nerve roots in your lower spine. The sciatic nerve is the longest nerve in your body, running from your lower back through your hips and buttocks and down each leg. When something compresses or inflames it near its origin, you feel pain that can radiate all the way from your lower back to your foot. The most common culprit is a herniated disc in the lumbar spine, but several other conditions can produce the same signature shooting pain.
Herniated Discs Are the Most Common Cause
A herniated disc happens when the soft, gel-like center of a spinal disc pushes through a crack in its tougher outer layer and presses against a nearby nerve root. This is the single most frequent reason people develop sciatica. About 95% of lumbar disc herniations occur at the two lowest disc levels in your spine: between the fourth and fifth lumbar vertebrae, or between the fifth lumbar vertebra and the sacrum (the triangular bone at the base of your spine). The L5-S1 level is the most common site overall.
These lower discs bear the most mechanical stress during bending, lifting, and sitting. Over time, the outer layer of the disc weakens, making it more vulnerable to bulging or rupturing. A herniation doesn’t always cause pain on its own. It becomes a problem when the protruding material contacts or compresses a nerve root, triggering inflammation that produces the burning, shooting, or electric-shock sensation down your leg.
Spinal Narrowing and Vertebral Slippage
As you age, the structures in your spine gradually wear down, and two conditions in particular can squeeze the sciatic nerve roots. Spinal stenosis is a narrowing of the spinal canal itself, leaving less room for the nerves that pass through it. This tends to develop slowly, and many people notice that their leg pain worsens with walking or standing and eases when they sit down or lean forward.
Spondylolisthesis is a related condition where one vertebra slides forward over the one below it. Degenerative spondylolisthesis, the most common type, happens when the discs between your vertebrae thin out with age, creating enough looseness for a vertebra to shift out of alignment. That shift can put direct pressure on the sciatic nerve roots. Both of these conditions tend to cause more gradual, chronic symptoms compared to the sudden onset of a herniated disc.
Piriformis Syndrome: A Muscular Mimic
Not all sciatic pain starts in the spine. The piriformis is a small muscle deep in your buttock that sits right on top of the sciatic nerve. When this muscle becomes tight, inflamed, or goes into spasm, it can compress the nerve and produce pain that feels a lot like spinal sciatica. The key difference is location: piriformis syndrome causes pain concentrated in the buttock and sometimes radiating down the back of the thigh, rather than originating in the lower back.
This condition is notoriously difficult to diagnose because there’s no single definitive test for it. Doctors typically identify it by ruling out spinal causes through imaging and by performing physical maneuvers that stretch and rotate your hip to see which movements reproduce the pain. Piriformis syndrome is more common in people who sit for long periods, runners, and those who’ve had a fall or direct trauma to the buttock.
Pregnancy and Sciatic Pain
Pregnancy creates a unique set of conditions that can trigger sciatica. Your body releases a hormone called relaxin, which loosens the tendons and ligaments in your joints to prepare for delivery. While necessary, this loosening can reduce the stability around your spine and pelvis, allowing structures to shift in ways that irritate the sciatic nerve.
At the same time, your center of gravity moves forward as your belly grows. Your spine compensates by increasing its curve, which changes how weight is distributed across the lower back. Both of these shifts can put pressure on the sciatic nerve. Pregnancy-related sciatica is most common in the second and third trimesters and typically resolves after delivery, though the discomfort can be significant while it lasts.
Occupational and Lifestyle Risk Factors
Certain jobs and daily habits raise your chances of developing sciatica. Physically demanding work is a consistent risk factor. A systematic review in Occupational and Environmental Medicine found that higher physical workload predicted worse outcomes for people with sciatica, with a 19% increased odds of delayed return to work. Jobs that involve heavy lifting, frequent bending, whole-body vibration (like operating heavy machinery or long-haul driving), or prolonged sitting all put extra stress on the lumbar discs and surrounding structures.
Sedentary behavior outside of work matters too. Sitting for hours compresses the discs in your lower spine and tightens the hip flexors and piriformis muscle. Lack of core strength leaves the spine with less muscular support, making disc problems more likely. Smoking also increases the risk by reducing blood flow to the spinal discs, accelerating their degeneration.
What Sciatic Pain Feels Like
Sciatic pain is distinctive. It typically follows a path from the lower back or buttock down through the back of the thigh and sometimes into the calf or foot. Most people experience it on one side only. The sensation varies: it can be a deep ache, a sharp or burning pain, or a feeling like an electric shock. Some people also notice numbness, tingling, or muscle weakness in the affected leg.
Certain positions tend to make it worse. Sitting, coughing, sneezing, or bending forward often intensify the pain because these movements increase pressure on the lower spinal discs. Lying down or walking at a gentle pace sometimes provides relief, though this depends on the underlying cause. If spinal stenosis is the problem, for instance, walking may worsen symptoms while sitting helps.
How Doctors Figure Out the Cause
Diagnosis usually starts with a physical exam. One common test involves lying on your back while a doctor raises your straightened leg. If this reproduces your sciatic pain, it suggests a disc herniation is compressing a nerve root. This test has a pooled sensitivity of about 91%, meaning it catches most cases, but its specificity is only around 26%, meaning many people without a disc herniation will also test positive. In older adults over 60, the sensitivity drops to about 33%, making it less reliable in that age group.
If your symptoms are severe, persistent, or accompanied by neurological changes like progressive weakness, your doctor will likely order imaging. An MRI is the gold standard because it shows soft tissue structures like discs and nerves in detail. CT scans can also be useful, particularly for bony abnormalities. An electromyogram, which measures electrical activity in your muscles, can help distinguish piriformis syndrome from spinal causes.
When Sciatic Pain Is an Emergency
The vast majority of sciatica, while painful, resolves with time and conservative treatment. But a rare condition called cauda equina syndrome requires immediate emergency care. This happens when a large disc herniation or other lesion compresses the bundle of nerve roots at the very bottom of the spinal cord.
The warning signs are specific: sudden loss of bladder or bowel control, inability to feel that you need to urinate or have a bowel movement, numbness in the inner thighs or groin area, and rapidly worsening weakness in both legs. If left untreated, cauda equina syndrome can cause permanent paralysis, incontinence, and sexual dysfunction. If you notice any combination of these symptoms, go to the emergency room immediately. Early surgical decompression significantly reduces the risk of permanent damage.