Pain in the left side of your lower stomach usually points to a problem in the organs or structures housed in that area: the lower portion of the large intestine (specifically the sigmoid colon), the left ovary and fallopian tube in women, part of the urinary tract, or the muscles and connective tissue of the abdominal wall. The most common cause in adults over 50 is diverticulitis, while in younger women, ovarian cysts are a frequent culprit. Several other conditions can produce the same type of pain, and telling them apart often comes down to the specific pattern of your symptoms.
Diverticulitis
Diverticulitis is the single most common reason for sudden, significant pain in the left lower abdomen, especially if you’re over 50. Small pouches called diverticula form along weak spots in the colon wall over time. They’re extremely common with age and usually harmless. The trouble starts when one or more of these pouches becomes inflamed or infected, triggering an immune response that floods the area with blood and fluid. Because these pouches almost always develop in the lower left section of the colon, the pain lands squarely in that spot.
The pain can hit suddenly and feel intense right away, or it can start mild and build over several days. It often comes with fever, nausea, tenderness when you press on the area, and a noticeable change in bowel habits like sudden constipation or diarrhea. Uncomplicated cases, which make up the majority, can sometimes resolve without antibiotics in otherwise healthy people. More severe cases, or those in people with weakened immune systems, typically do require antibiotic treatment.
Ovarian Cysts and Other Gynecological Causes
If you have ovaries, a cyst on the left ovary is one of the most likely explanations for one-sided lower abdominal pain. Most ovarian cysts are small, produce no symptoms, and disappear on their own within a few menstrual cycles. A larger cyst, though, can cause a dull ache or sharp pain below the bellybutton toward one side. The pain may come and go rather than stay constant.
Two complications make ovarian cysts more serious. A large cyst can cause the ovary to twist on itself, cutting off its blood supply. This is called ovarian torsion, and it produces sudden, severe pelvic pain along with nausea and vomiting. A cyst can also rupture, causing sharp pain and internal bleeding. Both situations need prompt medical attention. Endometriosis, a condition where tissue similar to the uterine lining grows outside the uterus, can also form cysts on the ovary (called endometriomas) and cause recurring left-sided pain, particularly around your period.
For women of childbearing age, pelvic ultrasound is the preferred first imaging test because it can clearly visualize the ovaries and uterus without radiation exposure.
Kidney Stones Moving Through the Ureter
A kidney stone on the left side can cause pain that shifts location as the stone travels. It typically starts as flank pain, felt in the lower back below the rib cage. As the stone moves down the narrow tube connecting the kidney to the bladder, the pain migrates toward the lower abdomen. At this stage it can easily be confused with a stomach problem or even appendicitis. Once the stone reaches the lowest part of the ureter near the bladder, the pain often radiates into the groin or pelvic area.
Kidney stone pain tends to come in intense waves rather than staying constant. You might also notice blood in your urine, a frequent urge to urinate, or nausea. The key distinguishing feature compared to digestive causes is that kidney stone pain rarely comes with fever (unless there’s an accompanying infection) and often makes it impossible to find a comfortable position.
Inguinal Hernia
A hernia on the left side occurs when tissue, usually a loop of intestine, pushes through a weak spot in the abdominal wall near the groin. This is more common in men but can happen in anyone. The hallmark sign is a visible or palpable bulge in the lower abdomen or groin area, though the bulge isn’t always obvious.
What sets hernia pain apart is its strong relationship to activity and position. Symptoms get worse when you strain, lift something heavy, cough, or stand for a long time, and they tend to improve when you rest or lie down. A doctor can often diagnose a hernia during a physical exam by asking you to stand and cough while they feel for the bulge. If the diagnosis isn’t clear, ultrasound, CT, or MRI can confirm it.
Constipation and Gas
Not every left-sided pain signals something serious. The descending colon runs down the left side of your abdomen, and the sharp bend where it transitions into the sigmoid colon sits right in the lower left quadrant. Trapped gas or backed-up stool in this area can produce cramping, bloating, and surprisingly sharp pain. If your pain came on gradually and you haven’t had a normal bowel movement in a few days, constipation is a likely explanation. The pain usually resolves once you’re able to pass gas or have a bowel movement.
Irritable Bowel Syndrome
IBS frequently causes pain in the lower left abdomen because the sigmoid colon, which sits in that area, is one of the most active segments of the bowel. The pain is typically crampy, comes and goes over weeks or months, and is closely tied to bowel movements. It often improves after you pass stool. Unlike diverticulitis, IBS doesn’t cause fever, and the pain tends to be a recurring pattern rather than a sudden new symptom.
How Doctors Figure Out the Cause
A CT scan of the abdomen and pelvis is the gold-standard test for left lower abdominal pain, particularly when diverticulitis is suspected. It can identify inflammation, abscesses, kidney stones, and many other causes with very high accuracy. For suspected diverticulitis specifically, CT has sensitivity and specificity approaching 100 percent. It’s also useful because it can catch alternative diagnoses that mimic diverticulitis.
For younger women, doctors often start with a pelvic ultrasound instead, since gynecological causes are more likely and ultrasound avoids radiation. MRI offers excellent soft tissue detail without radiation but takes longer and costs more, so it’s typically reserved for situations where CT results are inconclusive or radiation needs to be avoided.
Signs You Need Emergency Care
Most left-sided lower abdominal pain resolves on its own or with straightforward treatment. But certain symptoms alongside the pain signal something that needs immediate evaluation:
- Severe pain that comes on suddenly or keeps escalating
- Fever or chills, which suggest infection or significant inflammation
- Blood in your stool or urine
- Vomiting blood
- Inability to pass gas or have a bowel movement, which can indicate a bowel obstruction
- Shortness of breath alongside abdominal pain
- Yellowing of the skin or eyes
Pain that keeps coming back over days or weeks, even if it’s mild, also warrants a medical evaluation. A pattern of worsening pain is more concerning than a single brief episode.