Causes of Sciatic Nerve Pain: What Irritates the Nerve

The causes of sciatic nerve pain are usually found in the lower back, where a disc, a narrowed canal or a bone spur presses on or irritates a nerve root. Less often the nerve is irritated in the buttock. The leg pain you feel is the nerve's message, and the real question is what is irritating it. This page walks through the common answers in plain words. It is information to bring to your clinician, not a diagnosis.

Sciatica names the path, not the reason

The sciatic nerve is the thickest nerve in the body. It starts as several smaller nerve roots that leave the lower spine, join together in the pelvis and run through the buttock, then down the back of the thigh. Just above the knee it splits into branches that reach the lower leg and foot.

"Sciatica" simply means pain along that path. Think of it like saying "my phone is ringing". It tells you the sound, not who is calling. The same leg pain can have different sources, so the word alone cannot tell you what to do.

Sciatica is also common. Over a lifetime, somewhere between 10% and 40% of people will have it at some point (StatPearls, 2024). So if this is you, you are far from alone, and most episodes ease with time.

Common causes of sciatic nerve pain in the spine

Most sciatica starts where a nerve root leaves the spine. Here are the usual suspects, roughly from most to less common.

• A disc pressing on a nerve root. Between each pair of vertebrae sits a disc, a soft cushion with a tougher outer wall. If part of the inner material pushes outward, it can crowd the nerve root beside it. People call this a slipped or herniated disc. For more on how that feels and what tends to help, see our guide to sciatic pain from a herniated disc.
• A narrowed spinal canal. The canal is the channel inside the spine that holds the nerves. Over the years it can become tighter, often from age related changes in the discs and joints. The nerves then have less room. Clinicians call this spinal stenosis. Walking or standing for a while often brings on the leg pain, and sitting or leaning forward often eases it.
• Bone spurs. These are small extra growths of bone that can form at worn joints. If one grows near the exit gate of a nerve root, it can narrow that space. Spurs are common and often cause no pain at all.
• A slipped vertebra. Sometimes one vertebra sits a little forward on the one below it. This can narrow the openings where nerve roots pass out of the spine.

Notice the common thread. In each case, a nerve root has less space, or sits in a more irritated neighbourhood, than it would like.

Causes outside the spine, and why scans do not tell the whole story

Less often, the nerve is irritated further down its path. In the buttock it passes close to the piriformis, a small muscle deep in the hip. Some people have pain from tight or irritated tissue there, sometimes called piriformis syndrome. Opinions differ on how often this is the real cause, and it is probably less common than the spine. Our page on piriformis syndrome and sciatica pain explains the debate.

A long list of other reasons exists, such as an injury to the buttock, or a health condition that affects nerves. These are why a proper check matters.

Here is a point that surprises many people. A scan does not always explain the pain. Plenty of people with no leg pain have a bulging disc or a narrowed canal on their scan. Others have strong sciatica and a scan that shows very little. Images show structure. Pain also depends on how sensitive the nerve is, how inflamed the area is, and how your whole system is coping at that time.

So a scan is one piece of the puzzle. Your story, your examination and how things change over days and weeks matter just as much.

Why the question "what is irritating the nerve" helps

If sciatica names where the pain travels, the useful question becomes: what is irritating the nerve, and when does that change? The second half matters. Nerve irritation is often not constant. It tends to rise and fall with position, load and the time of day.

A disc problem often feels worse when you bend forward or sit for a long time. A narrowed canal often feels worse when you stand tall and walk, and better when you lean on a trolley. Buttock related pain may flare after sitting on a hard seat. None of these patterns is a rule, and they overlap. But they are clues, and a clinician can use them.

For a wider look at how nerve related back pain is understood, the Feldypedia article on sciatica and nerve related back pain is a good next read.

Warning signs that need care straight away

Most sciatica is not dangerous, but a few signs mean the nerves in the lower spine may be under serious pressure. If any of these appear, treat it as an emergency and get to an emergency department or call emergency services:

• numbness in the area around the genitals or the bottom, where a saddle would sit, or a new change in sexual feeling
• new difficulty passing urine, or loss of control of the bladder or bowel
• weakness, numbness or pain in both legs
• a leg that suddenly feels weak or is quickly getting weaker
• severe back pain after a serious accident, such as a car crash

Get same day medical care if you have a fever or feel generally unwell, if severe pain starts suddenly or gets worse quickly, if your pain began after a fall or a blow, or if you find you cannot lift the front of your foot. Book a doctor visit soon if you have lost weight without trying.

What a gentle, aware approach adds

In the Feldenkrais Method®, we do not try to force the nerve to behave. We explore how you move your pelvis, ribs, hips and back as one connected system. When a person holds the lower back still to protect it, the hips and ribs often do less, and the area stays guarded. Slow, easy movement within comfort lets you notice where you brace, and where you can let go a little.

Many people find this a calming way to relate to a sore back, and it sits comfortably alongside care from a doctor or physiotherapist. Feldy offers short guided lessons in this spirit. If you want a simple place to begin, try how to relax your back. You can also browse everything for the lower back on our lower back pain page.

One thing to notice this week

Over the next few days, watch your leg pain with curiosity. Which positions or moments make it ease, and which make it spread further down the leg? Sitting, standing, walking, lying on one side, getting out of a car, first thing in the morning?

Jot down a few notes in plain words. These details help your clinician far more than the word "sciatica" does, and they often point toward what is irritating the nerve.

Common Questions about causes of sciatic nerve pain (FAQ)

What is the cause of sciatic nerve pain?

There is no single cause for everyone. Most often a nerve root in the lower back is pressed or irritated, usually by a disc that has bulged out of place. A narrowed spinal canal, a bone spur or a slipped vertebra can do the same. Sometimes tight tissue in the buttock is involved. A clinician can help work out which fits you.

What causes sciatica to flare up?

Flares often follow a change in load or position, such as long sitting, lifting, a long drive or an awkward twist. Sometimes there is no clear trigger at all. Many people notice a pattern in which positions make the leg pain spread and which ease it. That pattern is useful information for your clinician.

Is sciatica a disease or a symptom?

Sciatica is a symptom. It describes pain that travels along the path of the sciatic nerve, usually from the lower back or buttock down one leg. The word does not say what is irritating the nerve. That is why the same word can describe quite different situations.

Why do I have sciatic nerve pain when my scan looks normal?

Scans show structure, and pain does not always follow structure. Many people with no pain have bulging discs on a scan, and some people with clear leg pain have a scan that shows little. Nerves can be sensitive for reasons an image cannot show, so the scan is read together with your story and an examination.

How long does sciatic nerve pain usually last?

The NHS describes recovery over several weeks up to a few months for most people, and some cases last longer. Staying gently active tends to be advised over long bed rest. If the pain is not changing, see a doctor. If a leg is getting weaker, get checked the same day, or go to an emergency department if it is happening quickly.

When is sciatic nerve pain a reason to get checked?

A doctor visit makes sense if leg pain lasts more than a few weeks, keeps returning or wakes you at night. Get checked the same day for weakness in the foot or leg. Call emergency services now, or head to the nearest emergency department, if the skin around your bottom or genitals goes numb, you start struggling to pass urine, you lose bladder or bowel control, or both legs turn weak, numb or painful.

How is nerve pain from the back different from a tight hamstring?

A tight or strained hamstring usually aches in the back of the thigh and stays local. Nerve pain often feels sharper or burning, may come with tingling or numbness, and can travel below the knee into the foot. If you are unsure which you have, ask a clinician to check.