Left-sided stomach pain has many possible causes, and the most likely explanation depends on exactly where you feel it. Pain in the upper left points to a different set of organs than pain in the lower left. In most cases, the cause is something common and treatable, like trapped gas, constipation, or a mild stomach issue, but certain patterns of pain signal something that needs prompt medical attention.
Upper Left vs. Lower Left: Why Location Matters
Your abdomen is divided into quadrants, and each one houses different organs. In the upper left, you’ll find your stomach, the tail of your pancreas (which sits tucked behind the stomach), and your spleen on the far left side. Your left kidney sits toward the back. In the lower left, the main player is the sigmoid colon, the S-shaped final stretch of your large intestine. For women, the left ovary and fallopian tube also sit in the lower left.
Pinpointing where the pain is strongest, whether it came on suddenly or gradually, and what makes it better or worse are the most useful clues for narrowing down the cause.
Common Causes of Upper Left Pain
Trapped Gas
One of the most frequent and least serious causes is gas getting stuck at a sharp bend in your colon called the splenic flexure, right beneath your left ribcage. Normally gas moves through this curve without trouble, but when too much gas builds up, it gets trapped at the bend, much like water backing up at a sharp turn in a river. This can cause bloating, pressure, and surprisingly intense pain that mimics more serious conditions. The pain usually improves after passing gas or having a bowel movement. Because the symptoms overlap with so many other problems, it can take time for doctors to land on this diagnosis.
Stomach and Pancreas Issues
Gastritis (inflammation of your stomach lining), ulcers, and acid reflux all produce pain in the upper left or upper middle abdomen that often worsens after eating. Pancreatitis causes upper belly pain that typically radiates to your back or shoulders. Acute pancreatitis pain can start mild and escalate, or hit suddenly and intensely, and it’s often accompanied by nausea, fever, and a tender abdomen. Pain that gets noticeably worse after meals is a hallmark of both acute and chronic pancreatitis.
Spleen Problems
Your spleen can become enlarged from infections or liver disease, producing pain or a feeling of fullness in the upper left belly. A distinctive feature of spleen pain is that it can spread to your left shoulder. Pain that gets worse when you take a deep breath is another red flag for spleen involvement. A ruptured spleen, sometimes caused by a blow to the abdomen, is a life-threatening emergency that causes dangerous internal bleeding.
Kidney Stones
A stone in your left kidney often causes pain in the lower back, side, or belly that can feel like it stretches from your groin to your flank. It’s commonly accompanied by nausea, vomiting, bloody or cloudy urine, pain while urinating, or a persistent urge to pee. Kidney stone pain tends to come in waves and can be extremely intense.
Common Causes of Lower Left Pain
Diverticulitis
Acute diverticulitis is the single most common cause of lower left abdominal pain in adults. It happens when small pouches that form in the colon wall (diverticulosis) become inflamed or infected. These pouches are extremely common: about 5 to 10 percent of people have them by age 45, and up to 80 percent develop them by age 80. Most people with pouches never have symptoms, but 10 to 20 percent eventually develop diverticulitis, and about a quarter of those will have it come back.
The classic signs are lower left pain, fever, and an elevated white blood cell count. The pain is usually steady rather than crampy, and it may build over a few days. Mild cases can be managed at home, while complicated cases may require a CT scan to check for abscesses or other problems.
Constipation
The sigmoid colon, where stool collects before a bowel movement, sits in the lower left. When stool backs up or moves slowly, it creates pressure and cramping right in that area. This is one of the most common explanations for lower left pain, especially if you haven’t had a bowel movement in a couple of days or your diet has recently changed. The pain usually eases after you go.
Inflammatory Bowel Disease
Conditions like ulcerative colitis and Crohn’s disease cause chronic inflammation in the intestinal lining. Lower left pain accompanied by diarrhea (sometimes bloody), urgency, and weight loss over weeks or months can point to inflammatory bowel disease. These conditions tend to flare and remit, so pain that comes and goes in a recurring pattern is worth mentioning to your doctor.
Causes Specific to Women
Several gynecological conditions produce pain in the lower left abdomen. Ovarian cysts on the left ovary can cause a dull ache or sudden sharp pain if the cyst ruptures or twists. Endometriosis, where tissue similar to the uterine lining grows outside the uterus, often causes chronic pelvic pain that may be worse around your period. Uterine fibroids can also create pressure and discomfort on the left side.
An ectopic pregnancy, where a fertilized egg implants outside the uterus (usually in a fallopian tube), causes sharp, localized pain that can become severe quickly. This is a medical emergency. Any sudden, intense lower abdominal pain during early pregnancy needs immediate evaluation.
How Doctors Figure Out the Cause
Your doctor will start with your symptom history and a physical exam, pressing on different areas of your abdomen to locate the pain and check for tenderness. Blood tests and a urine sample can help identify infection, inflammation, or kidney problems.
If imaging is needed, the choice depends on what your doctor suspects. CT scans offer the highest accuracy for most abdominal conditions in adults, with sensitivity between 90 and 100 percent and specificity between 95 and 97 percent for many diagnoses. Ultrasound is preferred for pregnant patients and children. For suspected diverticulitis, a CT scan is the standard tool to confirm the diagnosis and check for complications, especially if you’ve never had an imaging-confirmed episode before.
When Left-Sided Pain Is an Emergency
Most left-sided stomach pain resolves on its own or with simple treatment, but certain patterns need emergency care. Seek immediate help if your pain is sudden and severe, doesn’t ease within 30 minutes, or is accompanied by continuous vomiting. A swollen, tender abdomen with fever and a rapid pulse can indicate acute pancreatitis or another serious condition. Severe pain after an injury to your left side could mean a ruptured spleen, which causes life-threatening internal bleeding.
Pain combined with bloody stool, inability to pass gas, high fever, dizziness, or fainting also warrants urgent evaluation. For women of childbearing age, sudden sharp pelvic pain with vaginal bleeding or missed periods should be treated as an emergency until an ectopic pregnancy is ruled out.