Left-sided stomach pain has many possible causes, ranging from trapped gas to conditions that need prompt treatment. The left side of your abdomen contains your stomach, spleen, pancreas tail, left kidney, and parts of your colon, so pain in this area could originate from any of these organs. Where exactly the pain sits, whether it’s upper or lower, and what other symptoms come with it can help narrow down what’s going on.
Upper Left Pain: Common Causes
The upper left part of your abdomen houses your stomach, spleen, and the tail of your pancreas. It also contains a sharp bend in your colon called the splenic flexure, where your large intestine curves near the spleen. One of the most common and least serious causes of upper left pain is gas getting trapped at this bend.
This is sometimes called splenic flexure syndrome. Normally, gas moves through the curve without trouble, but when too much accumulates, it stretches the colon wall and causes sharp pain in the upper left abdomen, along with bloating, fullness, and sometimes nausea. Some people are born with an unusually tight bend in this part of the colon, making them more prone to the problem. The pain often resolves on its own once the gas passes.
Pancreatitis is a more serious possibility. Because the tail of the pancreas extends into the left upper abdomen near the spleen, inflammation here often produces severe upper abdominal pain that radiates to the back. The pain tends to feel like a deep ache, burning, or cramping, and it’s often hard to pinpoint exactly. Pancreatitis typically comes on after heavy drinking or as a complication of gallstones, and it usually requires medical attention.
Spleen problems, including an enlarged spleen or a splenic infarction (where blood flow to the spleen is blocked), can also cause upper left pain. These are less common but worth considering if the pain is persistent and accompanied by fatigue or feeling full after eating very little.
Lower Left Pain: Common Causes
The lower left abdomen is home to the sigmoid colon, the S-shaped section of your large intestine just before the rectum. This is the most frequent source of lower left abdominal pain, and diverticulitis is the leading culprit.
Diverticulitis happens when small pouches that form in the colon wall become inflamed or infected. These pouches are common after age 50, and when they flare up, the pain is usually sudden and concentrated in the lower left abdomen. It can start mild and worsen over days, or hit intensely right away. Fever, tenderness when you press on the area, nausea, and sudden changes in bowel habits (diarrhea or constipation) often accompany it. If you have steady lower left pain with a fever, that combination warrants medical evaluation.
Constipation is a simpler explanation that’s easy to overlook. Stool tends to accumulate in the sigmoid colon and rectum before a bowel movement, so when things are backed up, cramping and pressure often concentrate on the lower left side.
Kidney Stones
A stone in the left kidney or left ureter (the tube connecting your kidney to your bladder) can cause pain that starts in your lower back or side and radiates toward your lower abdomen and groin. The pain is often described as coming in intense waves, and it may shift location as the stone moves. Blood in the urine, nausea, and an urgent need to urinate are common alongside the pain.
Ovarian Cysts and Reproductive Causes
For people with ovaries, a cyst on the left ovary can produce a dull ache or sharp pain below the belly button on the left side, along with bloating and a feeling of pressure or heaviness. Most ovarian cysts are harmless and resolve without treatment. But a large cyst can cause the ovary to twist, leading to sudden, severe pelvic pain with nausea and vomiting. A cyst that ruptures can cause intense pain and internal bleeding. Both of these situations need immediate medical attention.
An ectopic pregnancy, where a fertilized egg implants outside the uterus (often in a fallopian tube), can also cause sharp one-sided lower abdominal pain. This is a medical emergency if accompanied by vaginal bleeding, dizziness, or shoulder pain.
Left-Sided Colitis
If your left-sided pain is chronic or keeps coming back with bloody diarrhea, left-sided ulcerative colitis is a possibility worth exploring. This form of inflammatory bowel disease involves continuous inflammation starting at the rectum and extending up to the splenic flexure. Symptoms include pain on the left side of the abdomen, bloody diarrhea, loss of appetite, and weight loss. Unlike a one-time stomach bug, the symptoms tend to recur over weeks or months, and diagnosis involves a colonoscopy.
How Doctors Figure Out the Cause
When you see a doctor for left-sided abdominal pain, the evaluation typically starts with a physical exam and questions about when the pain started, what it feels like, and what other symptoms you have. Imaging often comes next.
For upper left pain, a CT scan with contrast is the most reliable tool. It gives a detailed, high-resolution view of the spleen, pancreas, and surrounding structures, and it’s fast. Ultrasound is sometimes used as an initial screening step, particularly to check spleen size, but it’s less accurate than CT for most upper-left conditions. When there’s fever involved, CT is strongly preferred because ultrasound has poor sensitivity for detecting infections inside the abdomen. The American College of Radiology’s 2025 guidelines list CT as the appropriate first choice for most presentations of acute left upper quadrant pain.
For lower left pain, CT is also the standard when diverticulitis is suspected. Blood tests checking for signs of infection or inflammation help round out the picture.
Signs That Need Immediate Attention
Most left-sided abdominal pain turns out to be something manageable, like gas, constipation, or a mild infection. But certain combinations of symptoms signal something more urgent:
- Sudden, severe pain that stops you from standing upright or finding a comfortable position
- Pain with fever or chills, which suggests infection
- Blood in your stool or vomit, including stools that look black and tarry or vomit that resembles coffee grounds
- Rapid heartbeat, lightheadedness, or cold and clammy skin, which can indicate internal bleeding or shock
- Pain that steadily worsens over hours rather than coming and going
- A rigid, hard abdomen that is extremely tender to touch
Pain that lasts more than a few days without improvement, keeps returning, or comes with unexplained weight loss or new changes in bowel habits also deserves medical evaluation, even if it doesn’t feel like an emergency. People over 65, those who are pregnant, or anyone with a weakened immune system should have a lower threshold for seeking care.