Pain in the left side of your body can come from dozens of different structures, from your ribs and muscles near the surface to deep organs like your spleen, kidney, pancreas, and colon. The location, quality, and timing of the pain are the biggest clues to what’s behind it. Here’s a breakdown organized by region, from upper to lower, covering the most common and most important causes.
Upper Left Side: Stomach, Spleen, and Pancreas
The upper left portion of your abdomen houses part of your stomach, the tail of your pancreas, your spleen, and a bend in your colon. Problems with any of these can produce pain just below your left ribcage.
Pancreatitis is one of the more serious possibilities. The pancreas sits tucked behind the stomach, and when it becomes inflamed, it causes pain in the upper belly that often radiates to the back or shoulders. Eating typically makes it worse. Acute pancreatitis comes on suddenly and can be severe, while chronic pancreatitis produces a more constant, grinding pain that flares after meals. Gallstones and heavy alcohol use are the two most common triggers.
An enlarged spleen (from infection, liver disease, or blood disorders) can cause a dull ache or fullness under the left ribs. Gastric ulcers produce a burning or gnawing sensation in the same area, often connected to meals. And a condition called splenic flexure syndrome, where gas builds up at a sharp bend in the colon near the spleen, can cause surprisingly intense pain and bloating. That bend acts like a bottleneck. When too much gas tries to pass through, it stretches the colon wall and mimics something more alarming. It’s uncomfortable but not dangerous.
Lower Left Side: Colon and Diverticulitis
The most common cause of pain in the lower left abdomen in adults is diverticulitis. This happens when small pouches that form along the colon wall (diverticulosis) become inflamed or infected. Over half of all adults develop these pouches by age 60, and roughly 5% of those people will go on to develop diverticulitis at some point. Emergency department visits for diverticulitis have been rising steadily, increasing from 0.40% to 0.56% of all ED encounters over an eight-year period.
Diverticulitis typically produces steady, aching pain in the lower left abdomen, often with fever, nausea, and changes in bowel habits. Mild cases can be managed at home with rest and a temporary change in diet, but complicated cases involving abscess or perforation need more aggressive treatment. CT imaging with intravenous contrast is the standard way to confirm the diagnosis and check for complications.
Ulcerative colitis is another important cause of left-sided abdominal pain, particularly in younger adults. Most people are diagnosed before age 30. The inflammation in ulcerative colitis often follows a specific pattern: it starts in the rectum and extends upward through the sigmoid and descending colon, which sit on the left side. Left-sided colitis causes cramping, bloody diarrhea, urgency, and fatigue. In some cases, rectal bleeding or constipation is the only early sign.
Left Flank and Back: Kidney Problems
Your left kidney sits in the back of your abdomen, roughly at waist level. Kidney stones and kidney infections both produce pain in the back, side, or groin, but they feel quite different.
A kidney stone typically causes sudden, severe, cramping pain that comes in waves. It often starts in the flank and radiates downward toward the groin as the stone moves through the ureter. A kidney infection (pyelonephritis) produces a more constant, deep ache in the back or side, along with fever, chills, and painful or frequent urination. Cloudy, dark, bloody, or foul-smelling urine is a hallmark sign. Kidney infections usually start as a bladder infection that travels upward, and they need prompt treatment to prevent the infection from spreading.
Left Chest and Rib Area
Pain higher up on the left side, around the chest and ribs, brings a different set of possibilities. The one that worries most people is their heart, and that concern is sometimes warranted. A heart attack usually presents as pressure or pain over a wide area of the chest, not a single pinpoint spot. It can spread to the left arm, jaw, or back. Pericarditis, an inflammation of the sac around the heart, causes pain that worsens when lying down or breathing deeply and can radiate to the left shoulder and arm.
But chest wall pain is far more common. Costochondritis, an inflammation of the cartilage connecting your ribs to your breastbone, frequently occurs on the left side. It produces sharp or aching pain that worsens with deep breaths, coughing, sneezing, or any movement of the chest wall. The key difference from heart-related pain: costochondritis can usually be reproduced by pressing on the affected area. Heart pain cannot.
Lung-related causes include pleurisy (inflammation of the membrane around the lungs), which creates a sharp pain that gets worse when you breathe in or cough. A pulmonary embolism, a blood clot in the lung, also causes sharp pain that worsens with breathing, often accompanied by sudden shortness of breath. A pneumothorax (collapsed lung) produces sudden sharp pain in the chest, sometimes extending into the neck and shoulder.
Pelvic Causes in Women
For women, left-sided pelvic pain has a few additional possibilities tied to the reproductive organs. An ovarian cyst on the left ovary is one of the most common. The typical symptom is pain or pressure in the lower belly on the side of the cyst, either dull or sharp, and it may come and go. If a cyst ruptures, it can cause sudden, intense pain. Larger cysts can also press on the bladder, making it hard to empty completely, or cause pain in the low back and thighs.
Risk factors for ovarian cysts include endometriosis, polycystic ovarian syndrome (PCOS), pregnancy, fertility medications, and severe pelvic infections like chlamydia. An ectopic pregnancy, where a fertilized egg implants outside the uterus (usually in a fallopian tube), is a more dangerous cause of one-sided pelvic pain. It’s a medical emergency that requires immediate treatment.
Muscle and Nerve Pain
Not all left-sided pain comes from an organ. Strained abdominal or intercostal muscles, pinched nerves, and even shingles (which follows a nerve path on one side of the body) can all produce left-sided pain. The distinguishing feature of musculoskeletal pain is that it changes with movement and position. Bending, twisting, or pressing on the area usually makes it worse or reproduces it exactly. Organ pain, by contrast, tends to be deeper and less affected by body position.
Warning Signs That Need Urgent Attention
Most left-sided pain turns out to be something manageable, but certain patterns signal a potential emergency. Sudden, excruciating abdominal pain that comes on without warning raises concern for an aortic aneurysm rupture, internal hemorrhage, organ perforation, or loss of blood supply to part of the intestine.
Other red flags include a rigid abdomen that tightens involuntarily when touched, pain that gets sharply worse when you release pressure on the belly (rebound tenderness), pain that increases with coughing or tapping your heel on the ground, fever with a rapid heart rate, and any drop in blood pressure with lightheadedness. These signs suggest peritonitis, meaning the lining of the abdominal cavity is inflamed, and they typically require urgent evaluation or surgery. Absent bowel sounds, where the belly is completely silent, are particularly concerning when combined with severe pain.
How Left-Side Pain Gets Diagnosed
The diagnostic workup depends on where the pain is and what your other symptoms suggest. For lower left abdominal pain, CT with intravenous contrast is the most common first imaging test. It’s effective at confirming diverticulitis, identifying abscesses, and ruling out other causes. Ultrasound is often the first step for suspected ovarian cysts or kidney problems. MRI can provide a more detailed view when needed, particularly for inflammatory bowel conditions.
For suspected ulcerative colitis, colonoscopy allows direct visualization of the colon lining and biopsy of inflamed tissue. If the colon is too inflamed for a full colonoscopy, a flexible sigmoidoscopy, which only reaches the lower colon, may be used instead. Blood tests help check for infection, inflammation, hormone imbalances, and in the case of ovarian cysts, rule out pregnancy and bleeding. Simple abdominal X-rays are generally not useful as a first test for most left-sided pain, though they can help rule out a perforated colon or bowel obstruction in emergency settings.