Lower Back Pain Causes and What to Do First

The lower back carries the load and takes the damage. Most episodes are a strain or sprain of the muscles and ligaments around the lumbar spine — part of the roughly 90% of low back pain that StatPearls classifies as mechanical, against fewer than 5% to 10% caused by a specific spinal disease. That ratio is the reason the first move is care, not imaging.

What causes it, in rough order of frequency

MedlinePlus lists the causes of acute low back pain as:

• Muscle spasm, strain, or a tear in the supporting muscles and ligaments — the everyday cause.
• Herniated disc, when disc material presses a nerve root and the pain travels into the leg.
• Spinal stenosis, a narrowed canal that tends to hurt more standing and walking than sitting.
• Compression fracture of the spine, often from osteoporosis, and possible after minor force.
• Arthritis of the spine, and, rarely, spinal infection.
• Kidney stones or a kidney infection, which are not spinal at all.
• Pregnancy, and, rarely but seriously, abdominal aortic aneurysm.

Two of those shift by sex rather than by spine. Pregnancy is a recognized cause in women, and osteoporotic compression fracture is more common in women after menopause. The mechanical causes themselves are the same for everyone.

First-line care, per the ACP guideline

The American College of Physicians recommends starting acute and subacute low back pain without drugs: superficial heat, with massage, acupuncture, or spinal manipulation as further options. If you want medication, NSAIDs or skeletal muscle relaxants come first. Most people improve over time regardless of the intervention, which is what makes the low-risk options the right opening move.

For pain that has passed 12 weeks, the guideline reorders things: exercise, multidisciplinary rehabilitation, acupuncture, and mindfulness-based stress reduction come first; NSAIDs are the first-line drug; tramadol or duloxetine are second line; opioids come only after everything else has been tried and documented.

What to do in the first days

1. Cut back activity for a couple of days, not more. MedlinePlus is explicit that bed rest is not recommended and that you should stay as active as possible.
2. Ice for the first 48 to 72 hours, then heat.
3. Use an over-the-counter pain reliever such as ibuprofen or acetaminophen if you need one.
4. Avoid heavy lifting and twisting for about six weeks, even after the pain fades.
5. Rebuild with light aerobic activity after the first two to three weeks — walking, not a return to whatever caused it.

Why imaging usually waits

An MRI in the first weeks of ordinary low back pain rarely changes what is done, and it reliably finds disc bulges and degeneration in people who have no pain at all. NIAMS frames the trigger for evaluation as pain that persists beyond a few weeks, or pain arriving with something else — numbness and tingling, weakness, fever, unintended weight loss, trouble urinating, or a fall.

Red flags specific to the lumbar spine

StatPearls sorts them by what they are screening for:

Pattern	What it is screening for
New urinary retention, bowel dysfunction, saddle numbness, sciatica in both legs	Cauda equina syndrome
Progressive weakness or sensory loss, new incontinence	Neurologic compromise
Fever, recent spinal procedure, injected drug use, immunosuppression	Spinal infection
Cancer history, unexplained weight loss with focal tenderness	Malignancy
Major trauma, long-term steroids, osteoporosis, age over 70	Fracture

MedlinePlus adds pain traveling below the knee, weakness or numbness in the buttock, thigh, leg or pelvis, and pain still there after four weeks.

This content is informational and does not replace medical evaluation, diagnosis, or treatment. For the full map of causes across the spine see back pain causes, and for the kidney question specifically, kidney pain vs back pain.