Low back pain is most often caused by injuries to the bones, muscles, or nerves in the lower back but can also be related to other organs including the kidneys, colon, uterus, or pancreas.
Pain can spread across the entire lower back, or be felt on one side. If the left side of your lower back hurts, it’s important to understand what may be causing it—and when it might be a serious problem.
In this article, I’ll explain potential causes for pain in the left lower back, how these conditions are diagnosed, and when your pain may be an emergency.
Of the many potential causes of lower left back pain, these are some of the most common.
One of the most common causes of lower back pain on the left side is a muscle strain.
Muscle strains are caused by strenuous activities like lifting something heavy, twisting too hard, or participating in high-impact activities like sports.
These injuries can happen from something simple like moving boxes or something more serious such as a car accident.
Strains happen when the fibers in muscles stretch too far, which triggers inflammation and pain. Along with pain, a strain may also cause:
- Reduced range of motion
Acute, or short term, low back pain from muscle strain typically starts suddenly and can be accompanied by inflammation, redness, swelling, soreness, or bruising.
The severity of your strain determines how long it takes for your symptoms to subside, which can range from a few days to weeks.
You can generally treat a muscle strain at home with rest, ice, warmth, and over-the-counter treatments.
If the pain is severe, new symptoms develop, or does not resolve in a week, you should obtain medical care.
Sciatica is back pain that is triggered when the sciatic nerve gets inflamed.
This nerve originates at the base of the spinal column, then runs into the hips and buttocks, and down the leg. Typically with sciatica, the pain is worse on one side.
Sciatica can be caused when something pinches or puts pressure on the nerve.
Sciatica pain may feel electric, burning, or tingly.
At times, the pain may worsen with long periods of sitting or not changing positions. The pain is usually intense, and sharp, and radiates down your leg.—and may also affect your left lower back.
If symptoms such as problems urinating or numbness in the genital area are present, urgent medical care is needed.
Herniated or slipped disc
A herniated disc, also known as a slipped or ruptured disc, can cause intense pain in the lower back.
Between the bones (vertebrates) of your spine are cushioned discs that allow the bones of your spine to rotate and bend without rubbing against one another.
Sometimes, these discs can be pushed out of place by heavy lifting, bending, or for unknown reasons. The out-of-place disc is considered herniated or slipped.
When this happens, the bulge from the disc creates pressure on the nerves of the spine which results in pain.
A herniated disc is typically caused by trauma or excessive activity.
If you live a sedentary lifestyle or are overweight, you may also be at greater risk of getting a herniated disc.
The location and type of pain you experience depends on which part of your spine has been affected.
For example, herniated discs in the low back can create pressure on the sciatic nerve, triggering sciatica.
A herniated disc may also interfere with other muscles, nerves, or ligaments, causing symptoms like:
- Pain in the area of the disc
- Pressure in the lower back
- Numbness or tingling in the back
- Numbness or tingling that happens in the legs or other areas affected by the nerve
Pain that is severe enough to limit your ability to stand or walk should be evaluated by your healthcare provider.
Weight gain, changes in posture, and hormonal changes can all contribute to back pain during pregnancy. Pregnancy-related low back pain is especially prevalent during the second and third trimesters.
The extra weight of the baby and placenta puts extra pressure on your pelvic muscles, which are responsible for lower back support.
At the same time, pregnancy-related hormone changes can cause ligaments and joints in the pelvic area to loosen. Without as much support and with extra weight, this can lead to discomfort and back pain.
Other pregnancy-related factors that can cause low back pain include:
- Weakening abdominal muscles that result in less spine support
- Sacroiliac joint problems
- Kidney problems (urinary tract infections can be common in pregnancy)
Because urinary tract infections (UTI) can quickly lead to more serious kidney infections, all low back pain in pregnancy needs to be investigated.
Your provider may run urine tests to ensure that you do not have a UTI.
Treatment for back pain during pregnancy will vary depending on the individual’s current health status and medical history.
The healthcare provider may recommend exercises, supportive garments, over-the-counter medications, or prescription treatments.
Pregnancy body pillows and belly support bands may help address low back pain in pregnancy that is caused by poor spine support or relaxed ligaments.
Arthritis is a disorder that causes pain, swelling, and inflammation to the joints in the body. With some types of arthritis, there is breakdown to the bones and discs in the joints.
Arthritis commonly affects the lower back which results in pain.
Other signs of arthritis may include:
- Reduced range of motion
Arthritis typically affects older adults as a normal “wear and tear” of the joints due to aging, but anyone can experience low back pain from arthritis.
Sacroiliac joint dysfunction
The sacroiliac (SI) joints are in your pelvis, where the sacrum—a large bone composed of five bones that have fused together—connects with your two iliac bones, which make up your pelvis.
SI joint pain may occur on one or both sides of the body, but it typically affects one side of the lower back, as well as the buttocks.
If your left SI joint becomes affected, it can cause lower left back pain.
It may also cause trouble with movements including walking, standing, climbing stairs, squatting, or bearing weight on the impacted leg for too long.
While some SI joint dysfunction may resolve on its own, you may need physical therapy or other medical care to restore normal function and resolve symptoms.
Stress fractures can occur in the lower spine as a result of physical activity, sports, lifting weights, gymnastics, or other activities.
These fractures can also happen due to an injury, like a fall or a car accident.
Older adults and people with conditions like osteoporosis are more at risk,
Fractures may heal on their own over 6-8 weeks, but require medical care. Pain that is caused by a stress fracture is often severe and may require prescription medication.
Your healthcare provider will also monitor the healing progress.
Kidney stones are hard deposits of minerals—like calcium, phosphate, and magnesium—that form inside your kidneys.
Formation occurs when mineral content in the urine becomes too concentrated, leading to a buildup.
When the sharp, rigid surface of a kidney stone travels inside the kidney or begins transitioning into the bladder, it can be very painful.
This usually causes severe, crampy pain that comes and goes. Since the kidneys are located just below the ribcage on either side of the spine, it’s not uncommon for kidney stone pain to be experienced in the back. While it’s possible to develop stones in both kidneys, it’s more common to develop stones in one kidney.
In this case, you would experience pain in one side of your back—such as the lower left side.
It is not always clear what causes kidney stones, and some people may be more prone to them than others. If your back pain is severe, continues to worsen, or you have any of the other above symptoms, check in with your healthcare provider.
Most kidney stones will pass on their own with no specific treatment. In some cases, you may need a procedure to help you pass the stone, pain or nausea medication, or an antibiotic to treat infection.
Kidney infections occur when bacteria from the lower urinary tract spreads to the kidneys. Kidney infections can cause pain under your ribs in the mid-back or on either side of the lower back. The lower back pain can also radiate to the lower abdomen.
If your left kidney is infected, you’ll feel the pain on your lower left side. The pain may feel dull and achy at first, but it may also become sharp and stabbing.
Kidney infections can be serious if left untreated. If you experience low back pain on one side or the other along with any of the following symptoms, you may require immediate medical care:
- Frequent, painful urination
- Burning while urinating
- Feeling the need to urinate with a low urine output
- Foul-smelling urine
- Cloudy, dark, or bloody urine
- Fever and/or chills
- Nausea or vomiting
Untreated kidney infections can lead to severe infections and life-threatening complications.
It is important that you seek medical care if you are experiencing symptoms of a kidney infection.
Bright red blood in the urine, being unable to keep down fluids due to vomiting, fever over 101 degrees fahrenheit, severe low back pain, and the inability to urinate are all symptoms that need urgent medical attention at your nearest medical facility.
Endometriosis, a condition in which uterine tissue grows outside of the uterus, is often misunderstood and misdiagnosed.
This chronic condition affects more than 11% of American women between the ages of 15 and 44.
The exact cause of endometriosis is unknown but there are some things that increase the risk for developing it. Endometriosis can cause painful periods, fatigue, back pain, and infertility.
Lower back pain associated with endometriosis may be felt on the left side of the body or on both sides. The location of the pain can vary—it may be felt in the lower abdomen or pelvis, but it also may radiate down the buttocks and into the legs.
There’s also some research that has found endometriosis in the bones of the lower back. The pain typically gets worse around the time of your menstrual period.
Other signs of endometriosis can include:
- Heavy or clotty periods
- Extreme menstrual cramping
- Abdominal pain or intestinal cramping
- Painful bowel movements
- Pelvic pain
- Pain during sexual intercourse
- Spotting or bleeding between periods
- Trouble getting or staying pregnant
If you have symptoms of endometriosis, see your women’s health provider for a proper diagnosis.
Your pancreas makes insulin which manages the blood sugar level in the body. It is also an important digestive organ. When it becomes inflamed, this is known as pancreatitis.
Pancreatitis can be sudden, or it may slowly develop over time. It usually begins in the upper abdomen, and then can spread to the lower back.
The pain can last for hours or days with acute (short term) pancreatitis but can last a lot longer with chronic (long term) pancreatitis.
Other symptoms of pancreatitis may include:
- Stomach pain
Related illnesses, certain medications or excessive alcohol use can increase the risk of developing pancreatic disorders. Medical care is recommended for the treatment of Pancreatitis.
If you have low back pain on the left side, your healthcare provider r will perform a physical exam and run diagnostic tests to confirm the cause of your pain.
Tests used to evaluatelower left back pain may include:
- Blood tests to check your blood count and the functioning of your organs
- Urine tests to screen for signs of a kidney infection or kidney stone
- CT scans, X-rays, ultrasound, or MRI to look for physical abnormalities or injuries
When Is It An Emergency?
Lower left back pain can range from mildly uncomfortable to so severe pain that it ishard to function or move.
If you develop sudden, severe pain in your lower back, seek emergency medical care.
If the pain is milder, but does not resolve within 5-7 days, seek medical care.
If your symptoms worsen, are severe,or you also have fever andchills, go to the nearest medical facility and contact your healthcare provider.
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Frequently Asked Questions
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Mechanisms of low back pain: a guide for diagnosis and therapy. (2016).
Sprains and strains. (2017).
Herniated disk. (2021).
Pregnancy-related low back pain. (2011).
Sacroiliac joint pain — aftercare. (2021).
Kidney stones. (2016).
Kidney infection (pyelonephritis). (n.d.).
Pathophysiology and immune dysfunction in endometriosis. (2015).
Screening for malignancy in low back pain patients: a systematic review. (2007).