What causes most low back pain?

Most low back pain has no single identified cause

The World Health Organization (WHO) describes low back pain as pain between the lower edge of the ribs and the buttock. In about 90% of cases it is labeled non-specific, which means no particular disease or structural problem can be confidently named as the reason for the pain. That can feel unsatisfying, but it is the usual finding and does not mean something was missed.

The NHS puts it in plain terms: back pain can have many causes, it is not always obvious what causes it, and it often gets better on its own. Mayo Clinic adds that back pain often develops without a cause that shows up on a test or an imaging study. Pages such as Do I need an MRI or X-ray for back pain? explain why scans often add little in these cases.

Common explanations

A pulled muscle or overstretched ligament (a strain or sprain) is the cause named most often. MedlinePlus says sudden low back pain is most often due to injury to the muscles and ligaments that support the back, and that the lower back is the usual site because it supports most of the body's weight. The pain commonly starts just after lifting something heavy, moving suddenly or sitting in one position for a long time.

The US National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) lists further causes in three broad types. Mechanical or structural problems include worn or herniated discs (the cushion-like pads between the spinal bones, see What is a slipped disc?), spinal stenosis (a narrowing of the spinal canal, see What is spinal stenosis?) and fractured vertebrae. Inflammatory conditions include ankylosing spondylitis, a type of arthritis of the spine. Other medical conditions include osteoporosis, kidney stones and infections. NIAMS notes that several factors can be present at once and interact.

A finding on a scan is not always the answer. Mayo Clinic points out that a bulging or ruptured disc might not cause back pain, and that disc changes are often found on scans done for another reason. The page Are disc changes on an MRI normal? covers this in more detail.

What makes back pain more likely

For non-specific low back pain, WHO lists low physical activity, smoking, obesity and high physical stress at work as risk factors. NIAMS adds that poor sleep, depression or anxiety can make back pain more frequent and more severe, and that back pain becomes more common with age, particularly after 45. Genetics play a role in some of the disorders that cause back pain.

These are tendencies seen across large numbers of people. They do not predict what will happen to any one person, and having several of them does not mean pain is certain. For how the pain usually unfolds over time, see How long does back pain usually last? and the wider Back pain basics collection.

Rarer causes that clinicians check for

The NHS says that, very rarely, back pain can be a sign of a serious problem such as a broken bone, cancer or an infection. WHO describes this as specific low back pain, which can come from an underlying disease, tissue damage, or pain referred from another organ, for example the kidney or an aortic aneurysm (a bulge in the body's main artery). The warning signs that point to these causes are listed on When is back pain an emergency?

When to get help

The NHS advises seeing a GP if back pain does not improve after a few weeks of home care, stops you doing daily activities, comes with unexplained weight loss, a lump or swelling, or a change in the shape of the back, is worse at night or does not ease with rest, is worse when coughing or sneezing, or comes from the upper back between the shoulders. It advises an urgent GP appointment or a call to 111 for back pain with a fever or feeling generally unwell, or for severe pain that starts suddenly or worsens quickly. Pain or numbness in both legs, loss of feeling around the genitals or anus, changes in bladder or bowel control, chest pain, or pain after a serious accident need a 999 call or a visit to A&E. Services and advice differ between countries and between clinicians, so local guidance applies. This page is general education and is not personal medical advice.