What can cause pain in the lower left back?

The sources on this page do not list causes specific to the left side. Cleveland Clinic says strains and sprains are the most common causes of back pain. Other causes include a herniated disk pressing on a nerve, kidney stones or a kidney infection, and, as MedlinePlus lists, problems with the gallbladder, pancreas or female reproductive organs, or a leaking abdominal aortic aneurysm. Cleveland Clinic says gallbladder inflammation may cause pain in the upper right belly that may spread to the back.

How can I tell if it's my kidney or a muscle?

Cleveland Clinic says flank pain from a muscle strain usually feels like a dull ache and often gets worse with movements like bending, twisting or sneezing, while kidney pain doesn't usually get worse with movement and is usually felt on one side. The NHS lists a high temperature, pain or burning when you pee, and also aching muscles and flu-like symptoms among the symptoms of a kidney infection. A healthcare provider can check, and Cleveland Clinic lists blood and urine tests and imaging among the tests they may use.

When is lower left back pain an emergency?

The NHS says to call 999 or go to A&E (in the US, 911 or the emergency room) for back pain with pain, tingling, weakness or numbness in both legs, loss of feeling around the genitals or anus, changes in your bladder or bowels or in sexual function such as not being able to get an erection or orgasm, chest pain, or after a serious accident, and for a possible kidney infection with confusion, drowsiness or difficulty speaking. Cleveland Clinic says to call 911 for back pain with fever, nausea or vomiting, severe abdominal pain, numbness, tingling or weakness in an arm or leg, severe pain, spasms or weakness, loss of bladder or bowel control, trouble emptying your bladder, or problems walking, with balance or coordination.

Who should I see about one-sided back pain?

Cleveland Clinic says a healthcare provider can identify the cause of back pain. For a possible kidney infection, the NHS advises seeing a GP (a primary care doctor) for symptoms such as pain or burning when you pee, an urgent GP appointment or NHS 111 for signs such as a very high temperature or pain just under the ribs, and 999 for confusion, drowsiness or difficulty speaking; for kidney stones that are causing symptoms, it advises urgent medical help. For muscle pain in the flank, Cleveland Clinic says stretching, exercise and physical therapy can strengthen the muscles in your spine and help you avoid another injury. If a healthcare provider finds the pain is muscular, you can find physical therapists near you in the SpinalCare directory.

A woman pressing both hands against her lower back

Symptom guide · plain-English

Lower left back pain

Photo: Kindel Media / Pexels

Cleveland Clinic says strains and sprains are the most common causes of back pain, but pain on one side of the lower back can also come from organs such as the kidneys. None of the sources on this page lists a cause specific to the left side: they describe back pain, flank pain and kidney problems, and the signs that need a doctor.

Overview

Cleveland Clinic says strains (injuries to muscles or tendons) and sprains (injuries to ligaments) are the most common causes of back pain. MedlinePlus says sudden low back pain is most often caused by an injury to the muscles and ligaments that support the back.

Nerves can cause one-sided pain too. Cleveland Clinic notes that a herniated disk can press on nearby nerves, causing lower back pain and sharp, shooting pain down one side of your buttock and leg (sciatica).

So can organs. Cleveland Clinic describes flank pain, felt on the sides and back of the abdomen between the lower ribs and hips, and lists kidney stones, urinary tract infections and muscle strains among its common causes. It notes that most people have a kidney on either side of the spine and that kidney pain is usually felt on one side.

Cleveland Clinic says flank pain from a muscle strain often gets worse with movements such as bending, twisting, lifting heavy weights, laughing or sneezing, while kidney pain doesn't usually get worse with movement. The NHS also lists aching muscles and flu-like symptoms among the symptoms of a kidney infection. A healthcare provider can identify the cause, and Cleveland Clinic lists blood and urine tests and imaging among the tests they may order.

Common symptoms

With a back strain or sprain: muscle spasms, pain that gets worse when you move, and a reduced range of motion (Cleveland Clinic)
With muscle-related flank pain: usually a dull ache that often gets worse with specific movements or pressure on the area (Cleveland Clinic)
With sciatica: sharp, shooting pain down one side of the buttock and leg (Cleveland Clinic)
With a kidney infection, symptoms can include a high temperature, feeling or being sick, pain in your lower back or side, diarrhoea, aching muscles and flu-like symptoms, pain, burning or stinging when you pee, needing to pee more often and urgently than usual, and pee that's dark or cloudy (NHS)
With kidney stones: larger stones can cause severe pain that usually starts in the side of the tummy or the lower back, may spread to the groin, and may come and go; you may also have a high temperature or feel hot, cold or shivery, feel or be sick, need to pee often, or have cloudy pee (NHS)

Common causes

Back strains and sprains: Cleveland Clinic calls these the most common causes of back pain
A herniated disk pressing on a nerve, which can cause sciatica (Cleveland Clinic)
Spinal stenosis, and arthritic conditions such as osteoarthritis (MedlinePlus)
Kidney stones or a kidney infection (MedlinePlus), and other urinary tract infections (Cleveland Clinic)
Problems with the gallbladder or pancreas (MedlinePlus); Cleveland Clinic says gallbladder inflammation may cause pain in the upper right belly that may spread to the back
Conditions of the female reproductive organs, such as endometriosis or ovarian cysts, and problems related to pregnancy (MedlinePlus)
A leaking abdominal aortic aneurysm (MedlinePlus); Cleveland Clinic says an aneurysm can cause steady, deep pain in the lower back or belly, and you may also have pain in the leg, groin or pelvic area and a pulsing feeling in the belly. Cleveland Clinic says to call 911 for back pain with severe abdominal pain
Very rarely, back pain can be a sign of a serious problem such as a broken bone, cancer or an infection (NHS)

Warning signs to act on

Sources give different urgency for some of the same signs, such as fever. Each item says what its source advises, from emergencies to seeing a GP. For the emergency signs, the NHS says not to drive yourself to A&E: ask someone to drive you, or call for an ambulance.

Back pain with pain, tingling, weakness or numbness in both legs, loss of feeling around your genitals or anus, changes in your bladder or bowels, or changes in how your genitals feel during sex or not being able to get or keep an erection or to orgasm: the NHS says to call 999 or go to A&E (in the US, 911 or the emergency room)
Back pain with chest pain, or that started after a serious accident such as a car accident: the NHS says to call 999 or go to A&E
Back pain with fever, nausea or vomiting, severe abdominal pain, or numbness, tingling or weakness in an arm or leg: Cleveland Clinic says to call 911
Back pain with severe pain, muscle spasms or muscle weakness, loss of bladder or bowel control, trouble fully emptying your bladder, or problems walking, with balance or coordination: Cleveland Clinic says to call 911
A possible kidney infection with confusion, drowsiness or difficulty speaking: the NHS says to call 999 or go to A&E now
Back pain with feeling hot, cold, shivery or generally unwell, or severe pain that starts suddenly or gets worse quickly: the NHS advises an urgent GP appointment or help from NHS 111
A possible kidney infection with a very high temperature or feeling hot, cold or shivery, a very low temperature below 36C, pain in the lower tummy or in the back just under the ribs, blood in your pee, feeling or being sick, not having peed all day, or pregnancy: the NHS advises an urgent GP appointment or help from NHS 111, and says a kidney infection can be serious if it's not treated, as it can cause sepsis
Kidney stones that are causing symptoms: the NHS says to get urgent medical help, and to ask for an urgent GP appointment or help from NHS 111 if you're in severe pain or have a high temperature or feel hot, cold or shivery
Flank pain with blood in your pee, pain or burning when you pee, fever, chills or dizziness, nausea and vomiting, peeing more than usual, diarrhoea, constipation or bloating, headaches, or a skin rash: Cleveland Clinic says to call a provider right away
Back pain with a history of cancer, pain that is worse when you lie down or wakes you at night, redness or swelling on the back or spine, severe pain where you can't get comfortable, or unexplained fever: MedlinePlus says to contact your provider right away
Back pain with weight loss you haven't tried for, a lump or swelling in your back or a change in its shape, or pain that doesn't improve after resting or is worse at night: the NHS says to see a GP (a primary care doctor)
Back pain with weight loss you haven't tried for, steroid use or injected drug use, an episode that feels different and worse than before, or pain lasting longer than 4 weeks: MedlinePlus says to contact your provider

What usually helps

When it's a muscle or back problem

For back pain, the NHS advises staying active, not staying in bed for long periods, and using an ice pack or a heat pack wrapped in a tea towel. It lists anti-inflammatory painkillers like ibuprofen, which may not be suitable for everyone, and suggests checking with a pharmacist or GP if you're unsure which painkiller is suitable for you. The NHS advises not taking ibuprofen with a kidney infection unless a doctor advises it, and Cleveland Clinic says people with a history of kidney disease should avoid over-the-counter anti-inflammatory painkillers.

When it might be your kidneys

The NHS says the main treatment for a kidney infection is antibiotic tablets, that ibuprofen may increase the risk of further kidney problems, and that a kidney infection can be serious if it's not treated, as it can cause sepsis. For kidney stones that are causing symptoms, it says to get urgent medical help.

Exercise and physical therapy

The NHS suggests exercises and stretches for back pain, and says to stop if your pain gets worse and see a GP. For muscle pain in the flank, Cleveland Clinic says stretching, exercise and physical therapy can also strengthen the muscles in your spine and help you avoid another injury.

Getting it checked

For flank pain, Cleveland Clinic advises contacting a healthcare provider if it doesn't go away after about a day, goes away and comes back, is severe or comes on suddenly, or makes everyday activities difficult. For back pain, the NHS advises seeing a GP if it doesn't improve after treating it at home for a few weeks. The two sources set different timings: about a day for flank pain, a few weeks for back pain.

Watch: Mayo Clinic Health System on back pain

Understanding back pain: Causes, relief and prevention
Mayo Clinic Health System · Mayo Clinic Health System, published on Mayo Clinic's YouTube channel
A Mayo Clinic Health System video on the various causes of back pain, including arthritis, bulging or ruptured disks and muscle or ligament strains, and ways to find relief. For kidney and other causes, see the sections above. We embed it for general education.

Frequently asked

What can cause pain in the lower left back?: The sources on this page do not list causes specific to the left side. Cleveland Clinic says strains and sprains are the most common causes of back pain. Other causes include a herniated disk pressing on a nerve, kidney stones or a kidney infection, and, as MedlinePlus lists, problems with the gallbladder, pancreas or female reproductive organs, or a leaking abdominal aortic aneurysm. Cleveland Clinic says gallbladder inflammation may cause pain in the upper right belly that may spread to the back.
How can I tell if it's my kidney or a muscle?: Cleveland Clinic says flank pain from a muscle strain usually feels like a dull ache and often gets worse with movements like bending, twisting or sneezing, while kidney pain doesn't usually get worse with movement and is usually felt on one side. The NHS lists a high temperature, pain or burning when you pee, and also aching muscles and flu-like symptoms among the symptoms of a kidney infection. A healthcare provider can check, and Cleveland Clinic lists blood and urine tests and imaging among the tests they may use.
When is lower left back pain an emergency?: The NHS says to call 999 or go to A&E (in the US, 911 or the emergency room) for back pain with pain, tingling, weakness or numbness in both legs, loss of feeling around the genitals or anus, changes in your bladder or bowels or in sexual function such as not being able to get an erection or orgasm, chest pain, or after a serious accident, and for a possible kidney infection with confusion, drowsiness or difficulty speaking. Cleveland Clinic says to call 911 for back pain with fever, nausea or vomiting, severe abdominal pain, numbness, tingling or weakness in an arm or leg, severe pain, spasms or weakness, loss of bladder or bowel control, trouble emptying your bladder, or problems walking, with balance or coordination.
Who should I see about one-sided back pain?: Cleveland Clinic says a healthcare provider can identify the cause of back pain. For a possible kidney infection, the NHS advises seeing a GP (a primary care doctor) for symptoms such as pain or burning when you pee, an urgent GP appointment or NHS 111 for signs such as a very high temperature or pain just under the ribs, and 999 for confusion, drowsiness or difficulty speaking; for kidney stones that are causing symptoms, it advises urgent medical help. For muscle pain in the flank, Cleveland Clinic says stretching, exercise and physical therapy can strengthen the muscles in your spine and help you avoid another injury. If a healthcare provider finds the pain is muscular, you can find physical therapists near you in the SpinalCare directory.

Sources

This page organises information from the cited sources for general education. It is not medical advice and has not been reviewed by a clinician. Always consult a qualified clinician about your own care. Editorially reviewed October 6, 2026.