Back pain is extremely common - about 80 percent of people are affected at some point in their lifetime. Anyone can get back pain at any age, but it's more common in people over the age of 35.

Your back has many interconnecting structures including bones, joints, muscles, ligaments and tendons. Its main support structure is the spine, which is made up of 24 separate bones called vertebrae, plus the bones of the sacrum and coccyx. Between the vertebrae are discs that act as shock absorbers and allow your spine to bend. Your spinal cord threads down through the central canal of each vertebra, carrying nerves from your brain to the rest of your body.

Low back pain can happen anywhere below the ribs and above the legs. The lower back  is the connection between the upper and lower body, and it bears most of the body’s weight. So it's pretty easy to hurt your back when you lift, reach, or twist. In fact, almost everyone has low back pain at one time or another.

It's often very difficult to know exactly what causes back pain. It's usually thought to be related to a strain in one of the interconnecting structures in your back, rather than a nerve problem. For most people with back pain, there isn't any specific underlying problem or condition that can be identified as the cause of the pain. However, there are a number of factors that can increase your risk of developing back pain, or aggravate it once you have it. These include:
- standing, sitting or bending down for long periods
- lifting, carrying, pushing or pulling loads that are too heavy, or going about these tasks in the wrong way
- having a trip or a fall
- being stressed or anxious
- being overweight
- having poor posture.

There may be other, more serious underlying causes of your back pain, but these are rare. They include:
- fracture - a crack or break in one of the bones in your back
- osteoporosis - a condition where bones become weak, brittle and are more likely to break
- a slipped disc - this is when a disc bulges so far out that it puts pressure on your spinal nerves
- spinal stenosis - a narrowing of the spinal canal through which the spinal cord passes
- spondylolisthesis - when one of your vertebrae slips forward and out of position
- degenerative disc disease - when the discs in your spinal cord gradually become worn down
- osteoarthritis - a wear-and-tear disease affecting the joints between your vertebrae
- rheumatoid arthritis - an inflammatory condition in which your immune system causes inflammation of the lining of your joints and surrounding structures.

Back pain may also be caused by an infection or cancer, but these two causes are very rare.

If you have back pain, further testing is not normally recommended unless your symptoms don't improve after a few weeks or if you have one of the red flags [see box]. If your GP sends you for tests you may have:
- an X-ray
- a CT scan - a test that uses X-ray equipment and computer software to create images of the inside of your body
- an MRI scan - a test that uses magnets and radio waves to produce images of the inside of the body
- blood tests

These tests are used to find out if you have a more specific, underlying cause for your back pain.