Pain in the lower left side of your stomach typically involves one of a few common structures: the descending or sigmoid colon, the small intestine, or (in women) the left ovary and fallopian tube. The most frequent cause in adults over 40 is diverticulitis, but the list of possibilities ranges from trapped gas and muscle strain to conditions that need prompt medical attention. Where exactly the pain is, how it started, and what other symptoms you have all help narrow it down.
Diverticulitis: The Most Common Cause
Diverticulitis is the single most likely diagnosis when an adult has acute pain focused on the lower left abdomen. It happens when small pouches that form in the wall of the colon become inflamed or infected. These pouches develop most often in the sigmoid colon, the S-shaped segment that sits in the lower left part of your belly just before the rectum.
The pain can arrive in different ways. Sometimes it hits suddenly and intensely. Other times it starts mild and gradually worsens over hours or days, or fluctuates in severity. Along with the pain, you may notice fever, nausea, tenderness when you press on the area, and a sudden change in bowel habits like new diarrhea or constipation. Diverticulitis becomes more common after age 40, though younger adults can develop it too, particularly with a low-fiber diet or obesity.
Mild episodes are often managed at home with a temporary change in diet and sometimes antibiotics. More severe cases, especially those with high fever or signs of a perforation, may require hospitalization. A CT scan of the abdomen and pelvis is the gold standard for confirming the diagnosis, with an accuracy around 98%. It can also rule out complications like an abscess or a small hole in the bowel wall.
Gas, Constipation, and IBS
Not every pain in this area signals something serious. Trapped gas in the descending colon is one of the most common (and most benign) explanations. Gas pain tends to feel sharp or crampy, moves around, and improves after passing gas or having a bowel movement. Constipation can produce a similar aching or pressure on the left side because stool tends to accumulate in the sigmoid colon before a bowel movement.
Irritable bowel syndrome (IBS) frequently causes recurring pain in the lower left abdomen, often accompanied by bloating, alternating diarrhea and constipation, and discomfort that eases after using the bathroom. If your pain comes and goes over weeks or months and seems linked to stress, certain foods, or changes in your bowel routine, IBS is worth considering. It doesn’t cause fever, weight loss, or bloody stool, so those symptoms point toward something else.
Ulcerative Colitis and Left-Sided Colitis
Ulcerative colitis is a form of inflammatory bowel disease that specifically affects the colon. One common subtype, called left-sided colitis, involves continuous inflammation from the rectum up through the descending colon. This produces pain on the left side of the abdomen along with bloody diarrhea, urgency to use the bathroom, and sometimes weight loss or fatigue.
The key difference from IBS is that ulcerative colitis causes visible inflammation and often blood in the stool. It tends to follow a pattern of flares and remission. If you’re having persistent left-sided pain with bloody or mucus-filled stool, this is one of the conditions your doctor will want to evaluate, typically with blood tests and a colonoscopy.
Ovarian Cysts and Endometriosis
For women, the left ovary and fallopian tube sit in the lower left abdomen, and problems with either can cause localized pain. A cyst on the left ovary may produce a dull ache or sudden sharp pain, especially if it ruptures or twists. Many ovarian cysts are small, cause no symptoms, and resolve on their own within a few menstrual cycles.
Endometriosis is a condition where tissue similar to the uterine lining grows outside the uterus, often on the ovaries, fallopian tubes, or pelvic tissue. The hallmark is pelvic pain that’s far worse than typical menstrual cramping and tends to get worse over time. Pain during sex, pain with bowel movements or urination (especially around your period), and lower back pain are also common. Endometriosis can form cysts on the ovaries called endometriomas, which may cause persistent one-sided pain. Because the symptoms overlap with ovarian cysts, pelvic inflammatory disease, and other conditions, diagnosis often takes time.
Kidney Stones
A stone that forms in the left kidney and moves into the ureter (the tube connecting the kidney to the bladder) can cause severe pain that starts in the back or side below the ribs and radiates down into the lower abdomen. The pain typically comes in intense waves, and you may also have blood in your urine, nausea, or a frequent urge to urinate. Kidney stone pain rarely stays in one spot. It shifts and radiates as the stone moves, which helps distinguish it from problems with the colon or reproductive organs.
Inguinal Hernia
Men are 8 to 10 times more likely than women to develop an inguinal hernia, which occurs when a piece of intestine or fatty tissue pushes through a weak spot in the abdominal wall near the groin. The classic sign is a visible bulge near the pubic bone that becomes more obvious when you stand up, cough, or strain. You may also feel a burning or aching sensation at the bulge, along with pressure or discomfort in the groin that worsens with bending or lifting. In some cases, the hernia extends into the scrotum and causes swelling there. If the bulge can’t be pushed back in, becomes very painful, or you develop nausea and vomiting, the hernia may be trapped (strangulated), which requires emergency treatment.
Muscle Strain and Psoas Syndrome
Sometimes the pain isn’t coming from an organ at all. The psoas muscle runs deep through your pelvis and connects the lower spine to the thigh bone. A strain or irritation of this muscle can produce pain in the lower abdomen, groin, hip, or lower back that worsens with movement, particularly when lifting your knee toward your chest or standing from a seated position. Psoas syndrome is frequently misdiagnosed or missed because it mimics so many internal conditions, including kidney stones and even prostatitis. Your doctor typically diagnoses it by ruling out other causes first.
A pulled abdominal muscle from exercise, heavy lifting, or even a strong coughing spell can also cause sharp, localized pain on one side. Muscle-related pain usually gets worse when you tense your core (sitting up from lying down, for example) and improves with rest.
When Lower Left Pain Needs Urgent Attention
Most causes of lower left abdominal pain are manageable and not life-threatening. But certain patterns require immediate medical care. The American College of Emergency Physicians recommends seeking emergency help if your pain is sudden and severe, does not ease within 30 minutes, or is accompanied by continuous vomiting. Fever combined with worsening abdominal pain can signal a perforation or abscess. For women of childbearing age, severe abdominal pain with vaginal bleeding raises concern for an ectopic pregnancy, which is a medical emergency.
Constant, unexplained abdominal pain that comes with a fever and noticeable changes in your stool is also worth getting checked promptly, even if it doesn’t feel like an emergency. These symptoms together suggest inflammation or infection that benefits from early treatment rather than a wait-and-see approach.