Sciatic nerve pain is caused by anything that compresses, irritates, or inflames the sciatic nerve or the nerve roots in the lower spine that feed into it. The most common culprit is a herniated disc in the lumbar spine, but the list of causes runs from age-related wear and tear to muscle problems deep in the hip. About 40% of people in the U.S. experience some form of sciatica during their lifetime, and the risk climbs steadily with age.
Herniated Discs: The Most Common Cause
Between each vertebra in your spine sits a rubbery disc that cushions the bones. When the soft inner material of a disc pushes through a tear in its outer wall, it can press directly against a nerve root in the lower back. That nerve root is part of the sciatic nerve, which runs from the lower spine through the buttock and down each leg. The result is pain, numbness, or tingling that radiates along that path.
Compression alone doesn’t always cause symptoms, though. The herniated disc material also triggers a chemical inflammatory response. The body releases substances that irritate the nerve, amplifying the pain signal. This is why two people can have similar-looking disc herniations on an MRI but very different levels of pain: the combination of physical pressure and inflammation determines how much you feel.
Spinal Stenosis and Age-Related Narrowing
As the spine ages, the canal that houses the spinal cord and nerve roots gradually narrows. This process, called spinal stenosis, affects up to 95% of people by age 50 to some degree. Several things contribute. The discs between vertebrae dry out and flatten, reducing their cushioning effect. Cartilage wears down, and the body responds by growing extra bone (bone spurs) along the edges of the vertebrae. Those spurs can extend into the spinal canal, crowding the nerves.
The cramped space irritates or pinches the nerve roots that form the sciatic nerve, producing the same radiating leg pain as a herniated disc. Spinal stenosis tends to develop slowly, so symptoms often creep in over months or years rather than appearing suddenly.
Spondylolisthesis: A Slipped Vertebra
Spondylolisthesis occurs when one vertebra slides forward over the one below it. This misalignment can narrow the space where nerve roots exit the spine, putting direct pressure on them. Some people with a slipped vertebra never develop symptoms, particularly when the slip is minor. But when the shift is large enough to compress a nerve root, the result can be classic sciatica: pain shooting from the lower back into one leg.
This condition can stem from a stress fracture in the vertebra (common in young athletes who do repetitive extension movements like gymnastics), or it can develop gradually as the joints and ligaments of the spine weaken with age.
Piriformis Syndrome
Not all sciatic pain originates in the spine. The piriformis is a small, flat muscle that runs from the lower spine through the buttock to the top of the thigh. The sciatic nerve typically passes directly underneath it. When the piriformis swells, spasms, or tightens, it can compress the nerve right where it passes through the hip.
Common triggers include inflammation in or around the muscle, scarring from a previous injury, and prolonged sitting. In some people, the anatomy itself creates vulnerability. A person can be born with a sciatic nerve that takes an unusual path through the piriformis, or with a piriformis muscle that’s shaped in a way that crowds the nerve. Piriformis syndrome can be tricky to diagnose because it mimics spine-related sciatica almost exactly, but the source of compression is in the buttock rather than the back.
Diabetes and Nerve Damage
Chronically high blood sugar damages nerves throughout the body, and the sciatic nerve is no exception. Over time, elevated glucose interferes with the nerve’s ability to send signals properly. High blood sugar also weakens the walls of the tiny blood vessels (capillaries) that deliver oxygen and nutrients to the nerve. Starved of supply, the nerve deteriorates. This type of damage tends to affect the longest nerves first, which is why the legs and feet are usually hit earliest and hardest.
Diabetic nerve damage can produce symptoms that overlap with sciatica: burning, tingling, or shooting pain down the leg. The key difference is that it usually affects both sides of the body and worsens gradually, while spine-related sciatica more often hits one leg and can flare up suddenly.
Pregnancy
Pregnancy creates a perfect storm for sciatic nerve irritation. As the belly grows, the body’s center of gravity shifts forward, and the curve of the lower spine becomes more pronounced to compensate. That increased curvature puts extra pressure on the nerve roots in the lumbar spine. Hormonal changes also play a role: the hormone relaxin loosens tendons and ligaments throughout the body to prepare for delivery, which can allow joints in the pelvis and spine to shift enough to irritate nearby nerves.
During the second and third trimesters, the position of the baby itself can compress the sciatic nerve. Most pregnancy-related sciatica resolves after delivery as the mechanical and hormonal pressures ease.
Lifestyle Risk Factors
Certain habits and occupations raise the odds of developing sciatica. A large prospective study of middle-aged workers found that manual laborers had roughly double the risk of sciatica compared to managers and professionals. The connection held for both men and women, though the specific risk varied. Semi-professional occupations (jobs involving moderate physical demands) also carried elevated risk in men.
Excess body weight increases pressure on the spine and its discs. In the same study, women who were overweight had about 30% higher odds of developing sciatica, and those who were obese had 40% higher odds. Smoking was another significant predictor, raising risk by around 50% in women. Low levels of physical activity during leisure time also contributed. Previous episodes of low back pain or chronic neck pain were among the strongest predictors of future sciatica in both sexes, suggesting that existing spinal problems make the nerve roots more vulnerable over time.
How Sciatica Typically Resolves
Most episodes of acute sciatica improve significantly within four to six weeks. Research published in the British Medical Journal found that roughly 60% of patients recover within six weeks using conservative approaches: staying active, managing pain, and doing targeted exercises or physical therapy. Sciatica rarely appears before age 20 unless an injury is involved, and the single biggest risk factor is simply the cumulative effect of gravity on the lower back over the years.
Signs That Need Immediate Attention
In rare cases, a large disc herniation or other structural problem compresses the bundle of nerves at the base of the spinal cord, a condition called cauda equina syndrome. This is a medical emergency. The warning signs include sudden difficulty urinating or having a bowel movement, loss of bladder or bowel control, numbness spreading through the inner thighs and buttocks, and progressive weakness in one or both legs. These symptoms can develop alongside typical sciatica pain but represent a fundamentally different level of severity. If you notice them, go to an emergency room immediately, because delayed treatment can lead to permanent nerve damage.