Pain in the lower left side of your stomach most often comes from your colon, specifically from a condition called diverticulitis or from digestive issues like constipation and gas. But several other organs sit in that area, including part of your left kidney, your left ureter, and (in women) the left ovary and fallopian tube, so the list of possible causes is broader than you might expect. What’s going on depends a lot on how the pain feels, how suddenly it started, and what other symptoms came along with it.
Diverticulitis: The Most Common Cause
Small pouches called diverticula can form in the wall of your colon over time, and they tend to develop in the lower left section. Many people have these pouches without ever knowing it. But when one becomes inflamed or infected, that’s diverticulitis, and it’s the single most common reason for sharp pain in the lower left abdomen. The pain is usually sudden and intense, though it can also start mild and gradually worsen over hours or days. Along with the pain, you may notice fever, nausea, tenderness when you press on the area, and a change in your bowel habits like sudden constipation or diarrhea.
Diverticula become increasingly common after age 50, which is why lower left abdominal pain in middle-aged and older adults often points here first. Younger adults can develop diverticulitis too, but it’s less typical. Mild cases are usually managed at home with a temporary change in diet and a course of antibiotics, while more severe episodes, especially those with complications like an abscess, may need hospital care.
Gas, Constipation, and IBS
Before jumping to anything serious, it’s worth knowing that trapped gas and constipation are extremely common causes of lower left abdominal pain. The descending colon runs down the left side of your abdomen and takes a sharp turn near the bottom left before connecting to your rectum. Gas or stool that gets backed up in this bend can create cramping, bloating, and a dull or sharp ache that feels alarming but resolves once things move along.
Irritable bowel syndrome (IBS) is another frequent culprit. People with IBS commonly experience abdominal pain and cramping along with diarrhea, constipation, or both. The pain often flares after eating or during periods of stress and tends to improve after a bowel movement. IBS doesn’t cause visible inflammation in the digestive tract, which distinguishes it from inflammatory bowel disease (IBD). IBD, which includes Crohn’s disease and ulcerative colitis, causes similar cramping and diarrhea but also triggers fevers, bloody bowel movements, and weight loss. If you’re seeing blood in your stool or running fevers alongside your pain, that’s a meaningful difference.
Kidney Stones
A stone that forms in your left kidney may cause no symptoms at all while it sits in the kidney. The pain starts when it drops into the ureter, the narrow tube connecting your kidney to your bladder. A stone stuck in the left ureter causes serious, sharp pain in the left side and back below the ribs that spreads down into the lower stomach and groin. The pain comes in waves, shifting in intensity, and often changes location as the stone moves through your urinary tract. You may also feel the urge to urinate frequently, notice blood-tinged urine, or feel nauseous. Kidney stone pain is notoriously intense and usually sends people to the emergency room on its own.
Causes Specific to Women
In women, several reproductive organs sit in the lower left pelvis and can produce pain that feels like it’s coming from the stomach. Ovulation pain (sometimes called mittelschmerz) happens about two weeks before your period and causes a brief, sharp twinge on whichever side released an egg that month. Menstrual cramps can also be felt more on one side than the other.
An ovarian cyst on the left ovary can cause a persistent dull ache or, if it ruptures, sudden sharp pain. Endometriosis, a condition where tissue similar to the uterine lining grows outside the uterus, often causes chronic pelvic pain that worsens during periods. Pelvic inflammatory disease, usually resulting from an untreated sexually transmitted infection, causes lower abdominal pain along with unusual discharge, fever, and pain during sex.
Ectopic pregnancy is the most urgent possibility. This happens when a fertilized egg implants outside the uterus, typically in a fallopian tube. It causes one-sided lower abdominal pain that can become severe, sometimes with vaginal bleeding and dizziness. An ectopic pregnancy is a medical emergency because the tube can rupture.
Inguinal Hernia
An inguinal hernia occurs when tissue pushes through a weak spot in the lower abdominal wall near the groin. While these hernias develop on the right side more often than the left, they can happen on either side and are especially common in men. The telltale sign is a visible or palpable bulge in the groin area, accompanied by feelings of discomfort, heaviness, or a burning sensation. Symptoms tend to get worse when you strain, lift something heavy, cough, or stand for a long time, and they improve when you lie down.
Most inguinal hernias aren’t dangerous on their own, but a hernia that gets stuck (incarcerated) or loses its blood supply (strangulated) becomes an emergency. Warning signs include a bulge that suddenly gets larger or won’t push back in, severe tenderness, fever, nausea, and vomiting.
How Doctors Figure Out the Cause
When lower left abdominal pain is severe enough to warrant investigation, a CT scan of the abdomen and pelvis with contrast dye is the standard first-line imaging test. It’s the most useful examination for pinpointing what’s happening in this area and is particularly accurate for diagnosing diverticulitis and its complications. Ultrasound is sometimes used, especially in women when a gynecologic cause is suspected, but it’s less accurate for conditions like complicated diverticulitis, missing up to 80% of those cases in some studies. MRI generally isn’t helpful for the initial evaluation of acute abdominal pain because it takes longer, is more prone to motion artifacts in someone who’s in pain, and is less sensitive for detecting certain findings like free air or kidney stones.
Your doctor will also rely heavily on your description of the pain. Key details that help narrow the diagnosis: whether the pain came on suddenly or gradually, whether it’s constant or comes in waves, whether anything makes it better or worse, and what other symptoms are present. Fever and changes in bowel habits point toward diverticulitis or infection. Waves of pain radiating to the groin suggest a kidney stone. A bulge near the groin points to a hernia. Bloody stool raises concern for IBD or, less commonly, a vascular problem in the colon.
Signs You Need Immediate Care
Most lower left abdominal pain turns out to be something manageable, like gas, constipation, or a mild flare of a known condition. But certain combinations of symptoms call for urgent evaluation. Seek care right away if your pain is severe and unlike anything you’ve experienced before, if you can’t keep liquids down, if you have a fever alongside the pain, if you notice blood in your stool or urine, or if your abdomen becomes rigid and extremely tender to the touch. If you’ve had recent abdominal surgery and develop new pain with an inability to pass gas or have a bowel movement, that also warrants a trip to the emergency room. Sudden, severe one-sided pelvic pain in a woman who could be pregnant should be treated as an emergency until an ectopic pregnancy is ruled out.