Left-sided stomach pain has several possible causes, and the most likely one depends on whether the pain is in your upper or lower abdomen, how it feels, and how long it’s been going on. The left side of your abdomen houses parts of your stomach, colon, pancreas, left kidney, spleen, and (in women) the left ovary, so pain there can originate from any of these structures.
Upper Left Abdomen: What’s There
Your upper left abdomen contains your stomach, spleen, the tail of your pancreas, part of your colon, a portion of your small intestine, and your left kidney (which sits toward your back). Pain in this area most commonly comes from the stomach itself or from the portion of the colon that bends near your spleen.
Gastritis and stomach ulcers are two of the most frequent culprits. Both inflame your stomach lining, but they feel different. Gastritis causes a general burning or gnawing sensation between meals or at night. An ulcer produces a more intense, localized pain, often with a pattern of feeling very hungry one to three hours after eating. Ulcer pain tends to stay in one spot, while gastritis is more diffuse.
The spleen sits just under your left ribcage. Most people never feel it, but certain infections (mononucleosis is the classic example) can cause it to swell and ache. A more serious possibility is a splenic infarction, where blood flow to part of the spleen is cut off. That causes sudden, severe pain in the upper left belly that can spread to your left shoulder, sometimes with fever and nausea.
Lower Left Abdomen: Diverticulitis Is the Top Suspect
Pain that’s specifically in your lower left abdomen is most often related to diverticular disease. Diverticula are small pouches that form in the wall of your colon, and they overwhelmingly develop in the lower left section. When one of those pouches becomes inflamed or infected, that’s diverticulitis, and it typically causes steady, aching pain in the lower left that worsens over hours to days. You might also notice bloating, fever, nausea, or changes in your bowel habits.
Diverticulosis (having the pouches without inflammation) is extremely common. In the United States, fewer than 20 percent of people have it by age 40, but that number jumps to 60 percent by age 60. Most people with diverticulosis never develop symptoms. When they do progress to diverticulitis, a CT scan is the standard tool doctors use to confirm the diagnosis and check severity.
Constipation can also cause lower left pain, since stool tends to accumulate in the descending and sigmoid colon on that side. This pain is usually crampy and comes in waves as your colon contracts, and it resolves once you have a bowel movement.
Kidney Stones: Pain That Moves
A stone in your left kidney produces a distinctive pain pattern. It typically starts in your left flank (the area between your lower ribs and hip on your back) and migrates forward and downward as the stone travels through your urinary tract. The pain can feel like it extends from your side all the way to your groin. It’s often described as colicky, meaning it builds in waves, peaks, then eases slightly before surging again.
Kidney stone pain is hard to sit still through. People with it tend to shift positions constantly, trying to find relief. That restlessness actually helps distinguish it from other abdominal problems. Along with the pain, you might notice blood in your urine, pain when urinating, a persistent urge to urinate, nausea, or cloudy and foul-smelling urine. Fever or chills alongside these symptoms suggest the stone may be causing an infection.
Causes Specific to Women
If you have a uterus and ovaries, left-sided lower abdominal pain has additional possibilities. An ovarian cyst on the left side can cause a dull ache or sudden sharp pain if it ruptures or twists. Pelvic inflammatory disease, an infection of the reproductive organs usually caused by sexually transmitted bacteria, can produce one-sided or generalized pelvic pain along with abnormal discharge and fever.
Ectopic pregnancy is the most urgent concern. This happens when a fertilized egg implants outside the uterus, usually in a fallopian tube. If you’re of reproductive age, have missed a period, and develop sharp one-sided pelvic or abdominal pain (especially with vaginal bleeding or dizziness), this needs emergency evaluation. A ruptured ectopic pregnancy causes internal bleeding and can be life-threatening.
How Pain Quality Narrows the Cause
The character of your pain offers real clues. A burning sensation that’s worse on an empty stomach or between meals points toward gastritis or an ulcer. Crampy pain that comes and goes in waves suggests your colon (constipation, gas, irritable bowel) or a kidney stone. Sharp, sudden pain that stays constant is more concerning and can indicate something like a splenic problem, a ruptured cyst, or an obstruction.
Timing matters too. Pain that appears after meals and sits in your upper left abdomen is likely stomach-related. Pain that worsens over a day or two with fever leans toward diverticulitis or an infection. Pain that woke you from sleep or came on within seconds suggests something more acute, like a stone passing or a cyst rupturing.
Signs That Need Emergency Attention
Most left-sided abdominal pain turns out to be something manageable, but certain combinations of symptoms signal a serious problem. Get emergency care if you experience:
- Severe pain with a rigid abdomen. If your belly feels hard and board-like, and the pain worsens with any movement, this suggests peritonitis, an inflammation of the abdominal lining that requires urgent treatment.
- Pain with signs of shock. A racing heart, lightheadedness, cold or clammy skin, or confusion alongside abdominal pain can indicate internal bleeding or a ruptured organ.
- Abdominal distention. A belly that’s visibly swollen and tight, especially with vomiting and inability to pass gas, may point to a bowel obstruction.
- Vaginal bleeding with pelvic pain during early pregnancy. This combination raises concern for ectopic pregnancy.
One useful observation: if you’re lying completely still because any movement makes the pain worse, that pattern is associated with peritonitis. If you can’t stop moving and shifting because staying in one position is unbearable, that’s more typical of kidney stones or colicky pain. Neither pattern should be ignored if the pain is severe, but both give your doctor valuable information about what’s happening inside.
What to Expect at the Doctor’s Office
Your doctor will start by pressing on different areas of your abdomen to locate the pain precisely and check for tenderness, guarding (where your muscles tighten involuntarily when pressed), or rebound tenderness (pain that spikes when pressure is released). Where these findings show up helps narrow the diagnosis significantly.
For lower left pain in someone over 40 with fever, a CT scan is often ordered to evaluate for diverticulitis. For suspected kidney stones, imaging and a urine test are standard. Upper abdominal pain that persists may lead to blood work and potentially an upper endoscopy to look at your stomach lining directly. In women of reproductive age, a pregnancy test is almost always part of the initial workup for lower abdominal or pelvic pain, even if pregnancy seems unlikely.