Left lower back pain in females can stem from the same musculoskeletal issues that affect anyone, but several causes are unique to or more common in women. These include gynecological conditions like endometriosis and ovarian cysts, pregnancy-related joint changes, pelvic floor dysfunction, and hormone-driven ligament loosening. The location matters too: left-sided pain specifically can point to digestive issues in the sigmoid colon, a left kidney problem, or nerve compression affecting one side of the spine.
Muscle Strain and Disc Problems
The most common cause of left lower back pain in anyone is a musculoskeletal issue: a strained muscle, a sprained ligament, or a problem with one of the spinal discs. A herniated disc in the lower spine typically affects only one side. When the last lumbar nerve root (L5) is compressed, pain runs down the outside of the leg with numbness into the top of the foot. When the first sacral nerve root (S1) is compressed, pain travels down the back of the leg with numbness into the bottom of the foot.
L5 compression can cause weakness when you try to pull your foot upward toward your shin. In severe cases, this leads to foot drop, where your foot slaps the ground as you walk. S1 compression tends to weaken the motion of pushing your foot down, like pressing a gas pedal. If your left lower back pain shoots into your leg and comes with any of these patterns, a nerve root issue is likely.
Endometriosis and Ovarian Cysts
Endometriosis is one of the most overlooked causes of lower back pain in women, and it’s frequently mistaken for a musculoskeletal problem. The condition involves tissue similar to the uterine lining growing outside the uterus, where it can press on the bundle of nerves near the base of the spine called the lumbosacral plexus. That compression can produce low back pain, sciatica-like leg pain, and even neurological symptoms like numbness. The hallmark clue is that the pain is cyclic, worsening around your period.
Ovarian cysts can also cause pain in the low back or thighs. A cyst on the left ovary is more likely to produce left-sided symptoms. Most ovarian cysts resolve on their own, but a sudden, sharp increase in pain could signal a ruptured cyst or ovarian torsion (twisting), both of which need prompt medical attention.
Pelvic Floor Dysfunction
Your pelvic floor muscles work together with your abdominal and back muscles to stabilize your spine. When those muscles become overly tense or dysfunctional, they can send referred pain into the lower back. This is a common but underrecognized pattern in women.
Tight pelvic floor muscles tend to also be weak, because they’re stuck in a contracted state and can’t generate force effectively. Since these muscles all connect to the tailbone, which links directly to the spine, chronic tension there changes how your trunk manages pressure. That shift in pressure also affects your diaphragm (the main breathing muscle), which can alter your posture and contribute to an aching back. Pelvic floor physical therapy can address both the tension and the resulting back pain.
Pregnancy and Hormonal Joint Changes
During pregnancy, the body produces a hormone called relaxin that loosens muscles, joints, and ligaments so the pelvis can widen for delivery. Production can begin as early as 10 weeks into pregnancy. This loosening, combined with the extra weight in the pelvic region, makes the sacroiliac joints (the two joints connecting your spine to your pelvis) more mobile than they should be. The result is often one-sided lower back pain, sometimes radiating into the groin, thigh, or abdomen.
This pregnancy-related pelvic girdle pain can flare when climbing stairs, getting out of a car, rolling over in bed, or standing on one leg. The instability also raises your risk of sprains and injuries. Relaxin doesn’t drop back to pre-pregnancy levels immediately after birth. It can take up to 12 months for ligaments and joints to fully tighten again, which means postpartum women remain vulnerable to this type of back pain well after delivery.
Kidney Infections
A kidney infection (pyelonephritis) on the left side produces pain in the back, side, or groin that can easily be confused with a muscle problem. The key difference is the accompanying symptoms: fever, chills, frequent or painful urination, and urine that looks cloudy, dark, or bloody, or smells foul. Nausea and vomiting are also common.
Women are significantly more prone to urinary tract infections than men, and an untreated UTI can travel upward to the kidneys. If your left lower back pain came on relatively quickly and you have any combination of fever, urinary changes, or nausea, this is a cause worth ruling out quickly because kidney infections need antibiotic treatment.
Diverticulitis and the Sigmoid Colon
The sigmoid colon, the last segment of the large intestine before the rectum, sits on the lower left side of your abdomen. When small pouches in the colon wall become inflamed (diverticulitis), the pain is typically felt in the lower left abdomen. But that pain can also spread into the pelvis or radiate to the back, mimicking a musculoskeletal problem.
Diverticulitis usually comes with other digestive symptoms like changes in bowel habits, bloating, nausea, or fever. It’s more common after age 40 but can occur earlier. If left lower back pain coincides with lower left abdominal pain and digestive upset, the sigmoid colon could be the source.
Sacroiliac Joint Dysfunction
The sacroiliac (SI) joints bear the weight of your upper body and transfer it to your legs. Women’s SI joints are naturally more mobile than men’s, and hormonal fluctuations throughout the menstrual cycle can further affect ligament tension around these joints. This makes SI joint dysfunction a more frequent cause of one-sided lower back pain in women than in men.
SI joint pain is usually felt on one side of the lower back, just above the buttock, and can radiate into the hip or upper thigh. It often worsens with prolonged sitting, standing from a seated position, or climbing stairs. The pain can be difficult to distinguish from disc problems or hip issues without a targeted physical exam.
Red Flags That Need Urgent Attention
Most left lower back pain resolves with time, movement, and conservative care. But certain symptoms alongside back pain signal something more serious. Sudden loss of bowel or bladder control could indicate cauda equina syndrome, a rare condition where nerves at the base of the spine are severely compressed. This requires emergency treatment.
Other warning signs include fever combined with back pain (suggesting infection), progressive numbness or weakness in the legs, severe pain that doesn’t respond to rest or position changes, and unexplained weight loss accompanied by night sweats or fatigue. Any of these patterns warrants prompt evaluation rather than a wait-and-see approach.