Pain on the sides of your abdomen can come from your muscles, your digestive tract, your kidneys, or your reproductive organs. The cause depends heavily on exactly where the pain is, what it feels like, and what other symptoms come with it. Most side pain turns out to be something manageable, like trapped gas, a muscle strain, or a passing digestive issue, but certain patterns point to problems that need prompt attention.
Trapped Gas in the Colon
One of the most common and least worrisome causes of side pain is gas getting stuck in the bends of your large intestine. Your colon makes sharp turns near your ribs on both sides, and when excess gas builds up at these curves, it can cause surprisingly intense pain in the upper sides of your abdomen. The Cleveland Clinic compares it to what happens when heavy rain sends water rushing toward a sharp bend in a river: the gas overwhelms the curve and stretches the colon wall, which is packed with nerve endings.
This kind of pain tends to come and go, often feels like a cramp or pressure under the ribs, and usually improves after you pass gas or have a bowel movement. Some people are born with an unusually tight curve in the colon, making them more prone to this. If you notice the pain after meals, during periods of constipation, or when you’ve eaten gas-producing foods, trapped gas is a likely culprit.
Muscle Strain or Hernia
Your oblique muscles run along both sides of your abdomen, and they’re easy to strain during exercise, heavy lifting, or even a hard coughing fit. A strained oblique typically causes tenderness right at the surface, sharp pain when you twist or contract your core, and sometimes visible bruising or muscle spasms. The key clue is that the pain gets worse with specific movements and feels better when you’re still.
A hernia is different. Instead of a sudden sharp pain from overexertion, hernias tend to produce a deeper aching or burning sensation, sometimes with a visible bulge in the abdomen. The discomfort worsens with any activity that puts pressure on your core: lifting, running, or straining during a bowel movement. Hernias can also cause nausea. If you notice a lump or bulge alongside your side pain, that distinction matters because hernias sometimes need surgical repair.
Kidney Stones and Kidney Infections
Your kidneys sit in the back of your abdomen, just below the ribs on each side. When something goes wrong with a kidney, the pain often wraps from your back around to your side, sometimes radiating down toward your groin.
Kidney stones cause some of the most severe pain people experience. When a stone gets stuck in the tube connecting your kidney to your bladder, it blocks urine flow, causes the kidney to swell, and triggers intense spasms. The hallmark of kidney stone pain is that it comes in waves, varying in intensity, and typically hits one side at a time. You may also notice blood in your urine or pain when urinating.
A kidney infection (which often starts as a bladder infection that travels upward) produces side or back pain along with fever, chills, nausea, and a burning sensation when you urinate. Your urine may look cloudy or smell unusually strong. A kidney infection with high fever or bloody urine needs medical care quickly, since untreated infections can cause serious damage.
Digestive Causes by Location
The specific side that hurts narrows the possibilities considerably.
Left side, lower abdomen: The most common culprit here, especially in adults over 50, is diverticulitis. Small pouches called diverticula form in the lining of the colon (very common with age) and occasionally become inflamed or infected. The pain is usually sudden and concentrated in the lower left abdomen, and it may come with fever, nausea, and changes in bowel habits. Sometimes the pain starts mild and builds over hours or days.
Left side, upper abdomen: This area houses part of the stomach, the pancreas, and the spleen. Stomach inflammation, ulcers, indigestion, and pancreatitis can all produce upper left pain. Pancreatitis pain often feels like it bores straight through to your back.
Right side, upper abdomen: Gallbladder problems are the classic cause here. Pain from gallstones often flares after fatty meals and can radiate to your right shoulder blade. Liver issues can also cause pain in this area.
Right side, lower abdomen: This is the territory of the appendix. Appendicitis typically starts as vague pain around the belly button that migrates to the lower right over several hours, becoming sharper and more localized. It often comes with loss of appetite, nausea, fever, and an inability to pass gas. Appendicitis requires emergency treatment.
Reproductive Organ Pain
For people with ovaries, the lower sides of the abdomen are home to the ovaries and fallopian tubes, which means several reproductive conditions can cause side pain.
Ovulation pain (called mittelschmerz) occurs roughly 14 days before your next period and causes a one-sided ache or sharp twinge in the lower abdomen, on whichever side is releasing an egg that cycle. It can feel dull and crampy or sharp and sudden, sometimes with slight spotting. It’s harmless and usually resolves within hours, though for some people it can last a day or two.
Ovarian cysts, endometriosis, and pelvic inflammatory disease can also cause one-sided lower abdominal pain. An ectopic pregnancy, where a fertilized egg implants outside the uterus (usually in a fallopian tube), causes side pain that can become severe and is a medical emergency. If you’re of reproductive age and experiencing new, sharp one-sided pain with missed periods, dizziness, or vaginal bleeding, seek care immediately.
How to Tell Muscle Pain From Organ Pain
This distinction trips people up because both can feel intense. A few practical tests help sort them out. Try pressing on the painful area: muscle injuries are tender right at the surface and hurt more when you push on them. Organ pain tends to feel deeper and isn’t as easily pinpointed with a finger. Next, try changing positions, twisting your torso, or doing a gentle crunch. If the pain spikes with movement and fades at rest, muscles are likely involved. Organ-related pain often persists regardless of position, or comes in waves that have nothing to do with how you move.
Fever, changes in urination, blood in your stool or urine, or pain that wakes you from sleep all point away from a simple muscle issue and toward something internal.
When Side Pain Needs Urgent Attention
Most side pain resolves on its own or with basic care. But certain combinations of symptoms signal something more serious. Get to an emergency room if your pain is severe enough to prevent you from functioning normally, if you’re vomiting and can’t keep liquids down, if you have a fever along with the pain, or if you notice blood in your urine or stool. Pain that started like something you’ve experienced before but feels different this time, more intense or with new symptoms, also warrants a visit.
If kidney stones or another internal cause is suspected, the most common first imaging test is a CT scan of the abdomen without contrast dye. For pregnant patients, ultrasound is the preferred starting point. These scans are quick and give your care team a clear picture of what’s happening inside.