Sciatica: symptoms, causes and how it's diagnosed
Medically reviewed by Harvir Ubhi, Chartered HCPC Physiotherapist
Last reviewed: 16 September 2026
Sciatica is pain that follows the path of the sciatic nerve: it starts in your lower back and runs through your bottom and down the back of one leg, often reaching your foot or toes. It's not the same as general back pain, and recognising the difference matters, because the advice and the likely cause are different too.
This page covers what it actually feels like, what causes it, and how a GP or physiotherapist would diagnose it. If you already know you have sciatica and want the self-help stretches, our sciatica exercises guide has step-by-step instructions sourced from the NHS. A page like this can tell you what's likely going on, but it can't examine you. A trained physiotherapist can confirm the diagnosis properly and work out exactly what's causing yours, which matters because the right treatment depends on the specific cause.
What sciatica actually feels like
The pain sits mainly in your bottom and the back of one leg, often reaching down to your foot or toes. It usually affects one side, not both. People describe it as sharp or burning, and it often comes with pins and needles, numbness, or weakness in the leg. It tends to get worse when you move, sneeze, or cough, and it can start suddenly or build up gradually.
One useful way to tell it apart from ordinary back pain: if the pain stays in your back and doesn't travel down your leg, it's probably not sciatica. The leg pain is usually the dominant symptom, often worse than anything you feel in your back.
What causes it
Sciatica happens when the sciatic nerve gets irritated or compressed somewhere along its path. A slipped disc is the most common cause, especially as you get older. Spinal stenosis (narrowing of the space around the spinal nerves), spondylolisthesis (where one spinal bone slips forward over another), and back injuries can all cause it too.
How it's diagnosed
You don't need a scan for a GP or physiotherapist to diagnose sciatica. A clinical examination, based on your symptoms and a physical assessment, is enough to confirm it. X-rays and MRI scans are generally not needed, partly because spinal changes that show up on imaging are common at any age, including in people with no symptoms at all, so a scan often doesn't add useful information.
If you've been offered a scan and you're not sure why, it's a fair question to ask your physiotherapist or GP directly.
What usually happens next
Sciatica usually improves within a few weeks to a few months, though it can take longer and can come back. Movement helps more than rest does for most people. Our sciatica exercises guide covers the specific stretches, what to avoid, and when persistent symptoms mean it's time to see someone rather than keep self-treating.
When to get help urgently
Call 999 or go to A&E if you have sciatica and any of the following:
- Numbness around or under your genitals or bottom
- Loss of bladder or bowel control
- Severe pain or numbness in both legs
- Weakness in both legs that's bad enough to make it hard to stand
These can be signs of cauda equina syndrome, a rare but serious condition where nerves at the base of the spine are compressed. It needs same-day hospital assessment, not a routine appointment.
Frequently asked questions
How do I know if it's sciatica or just back pain?
Location is the main clue. Back pain stays in the back. Sciatica travels down through your buttock and leg, often past the knee, and the leg pain is usually worse than any pain in your back. If it's only in your back, sciatica is unlikely.
Do I need an X-ray or MRI to diagnose sciatica?
Usually not. A GP or physiotherapist can diagnose sciatica from a clinical examination alone. Imaging often isn't useful because spinal changes are common at any age, even in people without symptoms.
What's the most common cause of sciatica?
A slipped disc is the most common cause, and it becomes more likely as you get older. Spinal stenosis, spondylolisthesis, and back injuries are other causes.
How long does sciatica usually last?
Most cases improve within a few weeks to a few months. It can take longer, and it can come back. If it hasn't started improving after a few weeks of self-care, it's worth seeing a physiotherapist or GP.
Not sure who to see?
If you think you have sciatica and want a proper assessment rather than guessing, tell us your symptoms and we'll match you with the right London physio. Free, no obligation.
Get matched free →Sources: NHS (nhs.uk), Calderdale and Huddersfield NHS Foundation Trust. Fetched and checked 16 September 2026.