Left-sided stomach pain has a wide range of causes, from trapped gas to conditions that need prompt medical attention. Where exactly you feel the pain, whether it’s upper or lower, sharp or dull, helps narrow down what’s going on. Your left side houses your stomach, spleen, pancreas, left kidney, part of your colon, and in women, the left ovary and fallopian tube.
Upper Left Pain: Stomach, Spleen, and Pancreas
Your upper left abdomen sits just below and behind your ribs. The organs packed into this area include your stomach, the tail of your pancreas, and your spleen. Pain here often points to one of these structures.
Gastritis, or inflammation of the stomach lining, is one of the most common culprits. It typically produces a gnawing or burning ache in your upper belly that may get worse or better after eating. Overuse of pain relievers like ibuprofen, heavy alcohol intake, and a bacterial infection called H. pylori are frequent triggers. Left untreated, gastritis can progress to peptic ulcers, which are open sores in your stomach lining caused by acid erosion or that same bacterial infection. Ulcer pain tends to be more intense and localized than the vague discomfort of mild gastritis.
Pancreas problems can also radiate to the upper left abdomen or straight through to your back. Pancreatitis, inflammation of the pancreas, often comes on suddenly with severe pain after heavy drinking or as a complication of gallstones. The pain is usually steady rather than crampy and can feel worse when lying flat.
An enlarged or injured spleen is a less common but important cause of upper left pain. Infections like mononucleosis and liver disease can swell the spleen enough to cause a dull ache under your left ribs. A splenic infarction, where blood supply to part of the spleen is cut off, causes sudden, severe upper left pain that may spread to your left shoulder. This is rare, but it can signal a serious underlying condition like a blood disorder or heart disease.
Trapped Gas at the Splenic Flexure
One surprisingly painful yet harmless cause of upper left abdominal pain is splenic flexure syndrome. Your colon makes a sharp bend near your spleen as it transitions from the transverse colon to the descending colon. Gas normally passes through this curve without issue, but when too much accumulates, it gets trapped at the bend and stretches the colon wall. The result can be sharp, alarming pain in your upper left abdomen along with bloating.
The fix is usually dietary. Reducing high-fiber foods that produce excess gas, carbonated drinks, and other triggers often resolves the problem entirely. Keeping a food diary for a week or two can help you pinpoint which foods set it off. For many people, once they identify and avoid their triggers, the pain stops coming back.
Lower Left Pain: Diverticulitis and the Colon
Pain in the lower left abdomen has a different set of likely causes, and diverticulitis tops the list. It is the most common cause of acute lower left abdominal pain in adults. Diverticulosis, the formation of small pouches in the colon wall, affects 5 to 10 percent of people by age 45 and up to 80 percent by age 80. Most people with these pouches never have symptoms. But in 10 to 20 percent, one or more pouches become inflamed or infected, causing diverticulitis.
The classic pattern is left-sided lower belly pain combined with fever. The pain is usually constant rather than coming and going, and it can worsen over hours. About 25 percent of people who have one episode of diverticulitis will have another. CT scanning is the preferred way to confirm the diagnosis because it can directly visualize the inflammation inside and outside the colon wall, with reported sensitivity and specificity as high as 100 percent.
Other colon-related causes of lower left pain include constipation (hard stool building up in the descending colon), irritable bowel syndrome, and inflammatory bowel disease like ulcerative colitis or Crohn’s disease. These tend to involve changes in bowel habits, cramping that comes and goes, or pain that improves after a bowel movement.
Kidney Stones
A stone forming in or passing through the left kidney or ureter can cause pain that radiates from your lower back and side into your lower abdomen and groin. The pain is often described as one of the most intense people have experienced. It typically comes in waves as the ureter contracts to push the stone along, and it may shift location as the stone moves. You might also notice blood in your urine, nausea, or a frequent urge to urinate. Smaller stones often pass on their own within days to weeks, while larger ones may need medical intervention.
Causes Specific to Women
In women, the left ovary and fallopian tube sit in the lower left pelvis and can produce pain that feels like it’s coming from the stomach area. Ovarian cysts are fluid-filled sacs that form on or in the ovary, often during ovulation. Most are small and resolve without treatment, but a larger cyst that twists or ruptures can cause sudden, sharp pelvic pain on the affected side.
Ectopic pregnancy is a more dangerous possibility. This occurs when a fertilized egg implants outside the uterus, most often in a fallopian tube. Early signs can mimic a normal pregnancy: a missed period, breast tenderness, nausea. The first warning is usually light vaginal bleeding and pelvic pain. If the tube ruptures, it causes heavy internal bleeding with symptoms like extreme lightheadedness, fainting, and sometimes shoulder pain from blood irritating the diaphragm. This is a medical emergency. Severe pelvic pain with vaginal bleeding, especially if you could be pregnant, warrants immediate care.
Pain From the Abdominal Wall Itself
Not all left-sided pain comes from internal organs. Intercostal neuralgia, irritation of the nerves that run under your ribs, can produce pain in the chest, ribs, or upper abdominal area that wraps around in a band. It often worsens with movement, coughing, sneezing, or even deep breathing. This type of nerve pain can mimic organ problems convincingly, and it sometimes refers pain to the shoulder blade, back, or groin. A pulled abdominal muscle from exercise or heavy lifting can produce similar localized soreness that hurts more when you twist, bend, or tense your core. The key difference from organ pain: abdominal wall pain usually gets worse when you tighten your stomach muscles, while internal organ pain typically does not.
When Left-Sided Pain Needs Urgent Attention
Some patterns of left-sided abdominal pain call for immediate evaluation. Pain so severe it interrupts your ability to function, pain paired with vomiting that won’t stop or an inability to keep liquids down, or pain with complete inability to have a bowel movement all warrant an emergency visit. The same applies if you’ve had similar pain before but this episode is clearly worse or different in character.
Other red flags include fever with abdominal pain, blood in your stool or urine, signs of an ectopic pregnancy (pelvic pain with vaginal bleeding and a possible missed period), and symptoms of internal bleeding like lightheadedness, fainting, or a rapid heartbeat. If you’ve recently had abdominal surgery and develop new pain, that also merits prompt evaluation.