Pain along either side of your stomach typically comes from one of a handful of causes: trapped gas, a muscle strain, a kidney issue, or a problem with an organ in that specific area. The side matters. Your right and left sides house different organs, so the location of your pain is the single most useful clue for narrowing down what’s going on.
Right Side vs. Left Side: Why Location Matters
Your abdomen is divided into four quadrants, and each one contains a distinct set of organs. Your upper right side holds your liver, gallbladder, and the head of your pancreas. Your lower right side contains your appendix and the beginning of your large intestine. On the left, the upper quadrant holds your stomach, spleen, and part of the pancreas, while the lower left contains the descending and sigmoid portions of your colon. Both sides share a kidney toward the back.
When something goes wrong with one of these organs, pain tends to concentrate in the quadrant where it sits. That’s why a doctor’s first question is almost always “which side?” and “upper or lower?”
Common Causes of Right-Sided Pain
Upper Right: Gallbladder and Liver Problems
Upper right abdominal pain is most often related to the gallbladder or liver. Gallstones are one of the most frequent culprits. They cause a distinctive wave-like pain called colic, which happens when the gallbladder contracts and squeezes against a stone blocking its duct. This pain can be intense, often hitting after a fatty meal, and it may radiate into your right shoulder blade.
Gallbladder inflammation produces a more constant, tender pain in the same spot. Liver conditions, including fatty liver disease and various forms of hepatitis, can also cause a dull ache or sense of fullness under your right ribs.
Lower Right: The Appendix
Pain that settles in your lower right abdomen raises immediate concern for appendicitis. The classic pattern starts as a vague ache around the belly button, then migrates to a specific point in the lower right (known as McBurney’s point, roughly a third of the way from your hip bone to your navel). The area becomes increasingly tender, and pressing on it then releasing quickly causes a sharp spike in pain. If you tense your abdominal muscles involuntarily when the area is touched, that’s another warning sign.
Severe pain in this location warrants an emergency room visit. Appendicitis can progress to a ruptured appendix within hours, so it’s one situation where waiting it out is genuinely risky.
Common Causes of Left-Sided Pain
Upper Left: Trapped Gas
A surprisingly sharp pain under your left ribs is often just gas. Your colon makes a tight bend near the spleen called the splenic flexure, and gas can build up at this curve the same way water backs up at a sharp bend in a river. The result, sometimes called splenic flexure syndrome, is a stabbing pain in the upper left abdomen that can feel alarming but is usually harmless. It tends to ease after passing gas or having a bowel movement.
Lower Left: Diverticulitis
In adults over 50, sudden pain in the lower left abdomen is the hallmark of diverticulitis. Small pouches (diverticula) form in weak spots along the colon wall over time, and when one of these pouches becomes inflamed or infected, the pain can range from mild and gradually worsening to sudden and severe. Nausea, changes in bowel habits like unexpected diarrhea or constipation, and tenderness when the area is touched are common alongside the pain. Obesity and smoking increase the risk.
Pain on Either Side: Kidneys
Both kidneys sit toward the back of the abdomen, one on each side of the spine, just below the rib cage. Kidney stones produce pain when they move from the kidney into the ureter, the narrow tube connecting the kidney to the bladder. This pain is often described as excruciating, coming in waves, and radiating from the side of the back down toward the groin. It can shift location as the stone moves.
A kidney infection causes a more constant, deep ache in the upper back or side, often accompanied by fever, nausea, and painful urination. The key distinction from a muscle strain is that kidney pain doesn’t change much with body position or movement. Pressing on the muscles along your side won’t reproduce it, but tapping over the kidney area on your back will.
Muscle Strain: The Overlooked Cause
Not all side pain comes from an organ. The oblique muscles running along your sides can tear or strain, especially during sudden twisting, heavy lifting, or vigorous coughing. A muscle strain in this area comes on suddenly during the movement that caused it, and the pain is sharp and localized over the rib cage rather than deep inside the abdomen.
The easiest way to tell the difference: muscle pain gets worse when you move in specific ways, particularly repeating the motion that triggered it, or even just breathing deeply. It also hurts more when you press directly on the sore spot. Internal organ pain, by contrast, tends to be deeper, harder to pinpoint with a fingertip, and unaffected by changes in body position.
Ovulation Pain in Women
For women of reproductive age, a recurring one-sided pain that shows up mid-cycle is likely mittelschmerz, or ovulation pain. It occurs about 14 days before the next period when an ovary releases an egg, and the pain localizes to whichever side is ovulating that month. It can switch sides from cycle to cycle or stay on the same side for several months in a row.
The sensation ranges from a dull ache similar to menstrual cramps to a sharp, sudden twinge. It may come with light vaginal spotting. The pain usually resolves within a few minutes to a few hours, though it occasionally lingers for a day or two. Ovarian cysts can cause similar one-sided pain but tend to produce a heavier, more persistent ache.
When Side Pain Is an Emergency
Most side pain resolves on its own or turns out to be something manageable. But certain patterns signal a situation that needs immediate attention:
- Sudden, severe pain that comes on without warning and doesn’t let up within an hour.
- Pain with signs of shock, including a racing heart, sweating, confusion, or feeling faint.
- Rigid abdomen, where your stomach muscles tighten involuntarily and the area hurts more when you release pressure than when you press down.
- Lower right pain with fever and nausea, which suggests possible appendicitis.
- Pain after an injury to the left side, which could indicate a spleen problem.
Inflammation of the abdominal lining (peritonitis) causes constant pain that worsens with any movement, even a gentle touch or bump. This is always a medical emergency. If your pain fits any of these descriptions, go to an emergency room rather than waiting for a scheduled appointment.