Pain on the side of your stomach can come from dozens of different sources, but the most common ones are surprisingly ordinary. When researchers tracked diagnoses for adults who showed up with acute abdominal pain, gastroenteritis (a stomach bug) and nonspecific pain accounted for about 10% of cases each, followed by gallstones (4.5%), kidney stones (4.3%), diverticulitis (3.8%), and appendicitis (3.8%). That said, where exactly the pain sits, what it feels like, and what other symptoms come with it can narrow the list considerably.
What the Location of Your Pain Tells You
Your abdomen is roughly divided into four quadrants, and different organs live in each one. Pain in the upper right is often related to the gallbladder or liver. Pain in the lower right raises the possibility of appendicitis. Pain in the upper left points toward the stomach, spleen, or pancreas. And pain in the lower left is most commonly linked to diverticular disease, where small pouches form in the wall of the colon.
This mapping isn’t perfect, though. Kidney stones can cause pain on either side depending on which kidney is affected. Gas can mimic serious conditions: when it collects on the right side of the colon, it can feel like gallstones or appendicitis, and when it collects on the left, people sometimes mistake it for heart disease. A condition called splenic flexure syndrome happens when gas gets trapped at a bend in the colon on the left side and causes chronic discomfort.
Right Side Pain: Gallbladder and Appendix
The two organs that cause the most concern on the right side are the gallbladder (upper right, tucked under the ribs) and the appendix (lower right, near the hip bone). Gallbladder problems, especially gallstones and gallbladder inflammation, tend to produce pain after eating fatty meals. The pain sits high, just below the rib cage, and can radiate to the right shoulder blade. One classic sign of an inflamed gallbladder: if you press your fingers just below the right rib edge and try to take a deep breath, the pain will cut your breath short as the inflamed gallbladder pushes down against your fingers.
Appendicitis typically starts as vague pain around the belly button, then migrates to the lower right abdomen over several hours. It tends to get steadily worse rather than coming and going. If you have severe pain in the lower right side of your abdomen, especially with fever, nausea, or pain that intensifies when you move, walk, or cough, that needs urgent medical attention. Appendicitis is one of the most time-sensitive abdominal emergencies.
Left Side Pain: Diverticulitis and Constipation
Lower left abdominal pain in adults over 40 is frequently caused by diverticulitis. Small pouches called diverticula form in the colon wall over time (a condition called diverticulosis, which is extremely common and usually painless). When one of those pouches becomes inflamed or infected, the result is diverticulitis: a steady, sometimes severe pain in the lower left side, often accompanied by fever, nausea, and changes in bowel habits.
Constipation is another straightforward cause of left-sided pain. Stool tends to accumulate in the descending colon and sigmoid colon, both of which sit on the left side of your abdomen. The resulting pressure and distension can produce cramping that ranges from mild to surprisingly intense. This type of pain usually improves after a bowel movement.
Kidney Stones: Sharp Flank Pain That Moves
Kidney stones deserve their own section because the pain they cause is distinctive and often shows up on one side of the body. The classic presentation is a sudden onset of severe pain in the flank, the area between your lower ribs and your hip on one side of your back. As the stone moves through the urinary tract, the pain often shifts and radiates.
Stones near the top of the ureter (the tube connecting the kidney to the bladder) cause deep flank pain that stays in the back and side. As a stone moves lower, the pain tends to radiate forward and downward toward the lower abdomen. Stones near the bladder can cause pain that radiates into the groin, testicle, or labia. Many people also experience intense nausea, an urgent need to urinate, or blood in the urine. The pain typically comes in waves rather than staying constant.
Organ Pain vs. Muscle Wall Pain
One useful distinction is whether the pain is coming from an internal organ or from the muscles and tissues of your abdominal wall. Organ pain (called visceral pain) tends to feel dull, deep, achy, and hard to pinpoint. People describe it as crampy, squeezing, or gnawing, and it often seems spread across a general area rather than located at one exact spot. This is the kind of pain you feel with gas, bloating, gallbladder issues, or intestinal problems.
Pain from the abdominal wall itself, such as a pulled muscle or a bruised rib, feels different. Because your skin and muscles have a much denser network of nerves, this pain tends to be sharp, well-localized, and easy to point to with one finger. It usually gets worse when you tense your abdominal muscles, like when you sit up, twist, or cough. If you can reproduce the pain exactly by pressing on one specific spot, the cause is more likely to be in the muscle wall rather than an internal organ.
Side Pain Related to Reproductive Organs
For women and people with ovaries, side pain has additional possible causes that are easy to overlook. Ovulation pain (sometimes called mittelschmerz) occurs midway through the menstrual cycle when an egg is released, and it alternates sides month to month. It’s typically a brief, sharp twinge or a dull ache lasting a few hours to a day or two.
Ovarian cysts can cause a persistent ache or sudden sharp pain on one side of the lower abdomen, especially if a cyst ruptures or twists. Endometriosis and pelvic inflammatory disease can both produce side-localized pain that worsens during periods or with intercourse. An ectopic pregnancy, where a fertilized egg implants outside the uterus (usually in a fallopian tube), causes pelvic pain on one side that may be accompanied by light vaginal bleeding. If the fallopian tube begins to leak or rupture, the pain becomes severe and may be felt in the shoulder. This is a medical emergency.
When Side Pain Needs Urgent Attention
Most side pain turns out to be gas, a mild stomach bug, constipation, or a pulled muscle. But certain features signal something more serious. Pain that started mild and is steadily getting worse over hours is more concerning than pain that comes and goes. A rigid or distended abdomen, where the belly feels hard and tight rather than soft, is a red flag. Fever above about 101°F (38.5°C) alongside abdominal pain suggests infection or inflammation that may need treatment.
Other warning signs include vomiting blood, blood in your stool or urine, yellowing of the skin or eyes, pain that spreads upward toward the chest or shoulder, shortness of breath with the pain, and unexplained weight loss. Severe lower right pain with nausea and fever should be evaluated promptly to rule out appendicitis.
How Side Pain Gets Diagnosed
If your pain is persistent or severe enough to see a doctor, what happens next depends on where it hurts. For upper right pain, an ultrasound is typically the first imaging test, since it’s the best way to see the gallbladder and liver without radiation. For lower abdominal pain on either side, a CT scan is the preferred choice because it can visualize the appendix, colon, and reproductive organs with high accuracy. When the diagnosis isn’t clear from the location alone, CT is generally the go-to imaging tool.
Many cases of side pain, though, don’t need imaging at all. If your symptoms point clearly to gas, constipation, a stomach bug, or a muscle strain, your doctor may diagnose you based on your history and a physical exam. Imaging typically comes into play when the pain is severe, unexplained, or accompanied by the red-flag symptoms above.