Why Does Lower Back Pain Happen?

Lower back pain is one of the most common reasons people see a doctor, and one of the most common reasons they miss work. Most people will have at least one episode in their lifetime. The good news is that most episodes settle within a few weeks. The challenge is knowing what is causing your pain, what you can safely do about it, and when it needs a specialist's attention.

This guide explains how the lower back works, the most common causes of pain, the warning signs you should never ignore, and how lower back pain is diagnosed and treated.

How your lower back works

Your lower back, or lumbar spine, is made up of five large vertebrae stacked on top of each other. Between each pair sits an intervertebral disc, a tough outer ring with a soft, gel-like centre that acts as a shock absorber. Small joints at the back of the spine, called facet joints, guide movement and keep the spine stable.

Around this framework is a network of muscles, ligaments and tendons that hold you upright, help you bend and twist, and protect the spinal nerves. These nerves leave the spine through small openings and travel down into your buttocks and legs.

Because so many structures work together, pain can start in any of them: a muscle, a ligament, a disc, a joint or a nerve. That is why two people with "back pain" can have very different problems and need very different treatment.

The most common causes of lower back pain

Muscle and ligament strain

This is the most common cause. Lifting something heavy with poor technique, a sudden twist, or an unusual amount of activity can overstretch or tear muscle fibres and ligaments. The pain is usually felt across the lower back, may spread into the buttocks, and often comes with stiffness and muscle spasm. It usually improves steadily over days to weeks.

Poor posture and long hours of sitting

Sitting for long periods, especially slouched at a desk, on a motorbike, or looking down at a phone, places constant load on the discs and muscles of the lower back. Over time, this leads to aching, stiffness and fatigue in the back muscles. Office workers, drivers and students are especially affected.

Disc problems (slipped or bulging disc)

With age and repeated strain, the outer ring of a disc can weaken. The soft centre may bulge or push through, which is often called a slipped disc or disc herniation. A disc problem can cause back pain on its own, but if the disc presses on a nearby nerve it can also cause pain, tingling or numbness travelling down the leg. This is known as sciatica.

Wear and tear (degenerative changes)

As we get older, discs lose some of their water content and height, and the facet joints can develop arthritis. These changes are a normal part of ageing and often cause no symptoms at all. In some people, they lead to stiffness and pain that is worse in the morning or after rest.

Spinal stenosis

In spinal stenosis, the space around the spinal nerves narrows, usually because of thickened ligaments, bone spurs or bulging discs. It typically affects people over 50 and causes pain, heaviness or tingling in the legs when walking or standing, which eases when sitting or bending forward.

Other causes

Less common causes include a slipped vertebra (spondylolisthesis), fractures (particularly in people with weak bones from osteoporosis), inflammatory conditions of the spine, and, rarely, infection or tumours. Pain can also be referred to the back from the kidneys or abdominal organs, which is why a proper assessment matters.

Risk factors you can change

Some risk factors, such as age and genetics, are out of your control. Many others are not:

• Physical inactivity, which leaves the core and back muscles weak
• Excess body weight, which increases the load on the spine
• Long periods of sitting without breaks
• Poor lifting technique, especially bending and twisting at the same time
• Smoking, which reduces blood supply to the discs and slows healing
• Stress and poor sleep, which can make pain feel worse and last longer

When back pain needs urgent attention

Most back pain is not dangerous. However, some symptoms can signal a serious problem such as severe nerve compression, infection or a fracture.

Go to the emergency department straight away if back pain comes with loss of bladder or bowel control, numbness around the groin or inner thighs, sudden weakness in one or both legs, fever, or if it started after a serious fall or accident.

You should also book an appointment with a specialist soon if:

• Your pain has not improved after four to six weeks
• Pain travels below the knee, or you have numbness or tingling in the leg
• Pain is severe at night or wakes you from sleep
• You have unexplained weight loss, or a history of cancer
• You have osteoporosis or take long-term steroid medication

How lower back pain is diagnosed

Diagnosis starts with a careful conversation about your symptoms: when the pain started, what makes it better or worse, whether it spreads into your legs, and how it affects your daily life. This is followed by a physical examination to check your posture, movement, muscle strength, reflexes and sensation.

Imaging is not always needed. For most new back pain without warning signs, an X-ray or MRI does not change the treatment, and it can show age-related changes that are not actually causing the pain. Imaging is recommended when there are warning signs, when nerve symptoms are present, when pain does not improve with treatment, or when surgery or an injection is being considered.

• X-rays show the bones, alignment and signs of wear.
• MRI shows discs, nerves and soft tissues in detail.
• Blood tests may be used if infection or inflammation is suspected.

Treatment options

Treatment depends on the cause, but it almost always starts with the simplest, safest options.

Self-care and staying active

For most strains and new episodes, staying gently active is better than bed rest. Walking, light stretching and continuing normal activities as much as pain allows helps recovery. Heat packs can relax tight muscles, and short-term pain relief medication can make movement easier. Always follow your doctor's or pharmacist's advice on medication.

Physiotherapy and exercise

A structured exercise programme to strengthen the core, back and hip muscles and improve flexibility is one of the most effective long-term treatments. A physiotherapist can also correct posture and movement habits that keep the pain coming back.

Medication

Depending on your symptoms, your doctor may recommend anti-inflammatory medicines, muscle relaxants for a short period, or medicines that target nerve pain. These are chosen carefully based on your age, other health conditions and other medicines you take.

Interventional pain procedures

When pain persists despite these measures, image-guided procedures such as epidural steroid injections, nerve root blocks or facet joint injections can reduce inflammation around irritated nerves or joints. They can relieve pain enough for you to take part in rehabilitation.

Surgery

Surgery is needed only in a small number of cases: for example, when a disc is pressing on a nerve and causing progressive weakness, when severe sciatica does not improve with other treatment, or for significant spinal stenosis or instability. Modern minimally invasive spine surgery uses smaller incisions, which usually means less pain and a faster return to normal life.

Preventing back pain from coming back

• Take a short break to stand and move every 30 to 45 minutes when sitting
• Set up your workstation so the screen is at eye level and your lower back is supported
• Lift with your knees bent and the load close to your body, and avoid twisting while lifting
• Keep active with regular walking, swimming or other exercise you enjoy
• Do core-strengthening exercises a few times a week
• Maintain a healthy weight and stop smoking
• Sleep on a supportive mattress, in a position that keeps your spine neutral

The bottom line

Lower back pain is very common and usually improves on its own with time, movement and simple measures. But pain that lasts more than a few weeks, keeps returning, spreads into your legs, or comes with any warning signs deserves a proper assessment. Finding the exact cause is the first step towards treatment that works and lasts.