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A slipped disk means one of the disks in your spine has been damaged and may be pressing on a nerve. It can be very painful.

The good news is that the pain from a slipped disk generally gets better on its own within about six weeks.¹

Here we look at what happens when a disk in the lower part of your back is damaged.

• A slipped disk can cause severe back pain.
• Most people who have a slipped disk also get sciatica. Sciatica is a sharp, stabbing pain that runs down through one buttock and into one of your legs. It happens if the disk presses on a nerve.
• Slipped disks are not very common. Only about 1 in 25 people who have pain in their lower back caused by a physical problem have a slipped disk.¹
• Although it can be painful, a slipped disk isn't usually dangerous. It will probably get better on its own.²
• Surgery can help, but it's worth waiting awhile to see if you get better without it.²

Doctors call this condition a herniated disk. We've used the term slipped disk because that's what most people know it as, even though the disk has not really slipped at all. You may also hear people call it a ruptured diskor a disk prolapse.

Disks are part of your backbone, which is also called your spine. They are round pads of spongy tissue. Each disk has a tough outer ring and a soft jellylike center.

The disks lie between your vertebrae. The vertebrae are the 33 bones that make up your spine.

Each vertebra is linked to the next one by small joints that lock together. They are called facet joints. You can bend and twist your spine because of these joints.

The disks cushion the bones in your spine and keep them from being damaged when you jump or run.

Disks also allow the bones in your spine to flex when you move. This means you can bend over, arch your back and twist your body.

As well as supporting your body, your spine also carries a bundle of nerves from your brain to the base of your back. This is called the spinal cord.

The bones (vertebrae) that make up your spine have holes in the center. The holes make a tunnel all the way down your back. This is where your spinal cord fits.

Nerves coming out of the bottom of your spinal cord carry messages to your legs from your brain. Other nerves pass through small openings between the bones in your spine. These nerves branch off to every part of your body.

Your sciatic nerves are the main nerves in your legs. You have one in each leg. If you have a slipped disk, it can damage these nerves.

Your sciatic nerves are made up of smaller nerves that travel down your spine.

They run from the base of your back, to your buttocks and down the back of your thighs.

Above the back of your knees, they divide into two branches. These run down your legs to your feet.

Besides the bones, joints, nerves and disks in your back, you also have:

• Muscles
• Cartilage
• Tendons
• Ligaments.

These work together to allow you to bend, stretch and twist.

Sometimes a disk gets damaged. The disks that get damaged most often are the ones in the lower part of your back, especially the ones between the last five bones in your spine (in the lumbar region).

These disks are called the lumbar disks. They get damaged more often than other disks because they're under more pressure.

The tough outer ring of the disk tears and the jellylike center bulges through the tear in the disk.

The damaged part of the disk might press on the roots of the nerves coming out of the spinal cord. If it does, it causes pain and muscle weakness. It can also cause inflammation in your spine.

Each nerve goes to a different part of the body. So where you get pain from a slipped disk depends on which disk is damaged and which nerves it's pressing on.

When a disk in the lower part of your spine gets damaged, it's likely to press on the nerves near your spinal cord that become your sciatic nerves. That's why it can cause aching in your buttocks, thigh, legs and feet. This pain is often called sciatica.

Sometimes only a little bit of the disk bulges out of place. But if a lot of the disk gets damaged, it can put quite a lot of pressure on the nerves. Sometimes a piece of the disk may break off completely.³

As you get older, the disks in your back may begin to wear out. They become weaker, thinner and less spongy.⁴ If that happens, the outer ring of the disk is more likely to crack or tear. Then the center can bulge through more easily.⁵

The way you stand, sit and move can affect whether your disks get damaged. Having a job where you have to lift things a lot puts strain on the disks in your lower back.

We don't know for sure why some people get a slipped disk and others don't. But there are things that make it more likely. These are called risk factors. The most common risk factors are:

• Getting older
• Having a job where you do a lot of lifting
• Having a job where you have to sit for a long time
• Driving for many hours at a time
• Being very overweight
• Smoking
• Having spine problems in your family
• Being male
• Doing weight lifting-type sports.

To learn more, see Things that make a slipped disk more likely.

Most of us have pain in our lower back at some point in our lives. Usually, the problem gets better on its own within two weeks.¹

It can be difficult for doctors to pinpoint the exact cause of low back pain, even with the help of tests such as X-rays.

But most low back pain is not caused by a disk problem. Only about 1 in 25 people with low back pain caused by a physical problem have a slipped disk.¹ Low back pain is usually caused by a minor injury, such as a strained muscle or ligament.

To find out more, see our information on Back pain.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.