Stomach aches have dozens of possible causes, ranging from something as simple as eating too fast to serious conditions like appendicitis. Most of the time, the culprit is temporary: a viral infection, something you ate, stress, or a medication side effect. But where the pain sits, how long it lasts, and what other symptoms come with it can tell you a lot about what’s actually going on.
Infections: The Most Common Cause
Viral gastroenteritis, often called “the stomach bug,” is the single most common reason for sudden stomach pain with nausea, vomiting, or diarrhea. Noroviruses and rotaviruses are the usual culprits, spreading easily through contaminated surfaces, food, or close contact with someone who’s sick. The pain tends to feel like general cramping across the whole abdomen rather than a sharp pain in one spot.
Bacterial infections from contaminated food (Salmonella, E. coli, Campylobacter) cause similar symptoms but sometimes hit harder, with higher fevers and bloody diarrhea. Parasites and chemical contaminants in food can also trigger it. Most cases of gastroenteritis resolve on their own within a few days, though dehydration is the main risk, especially in young children and older adults.
What You Eat and Drink
Food intolerances are a sneaky source of recurring stomach pain because they don’t always cause dramatic symptoms. Lactose intolerance is one of the most widespread: when your body can’t break down the sugar in dairy, bacteria in your gut ferment it instead, producing gas, bloating, and cramping. The same thing happens with fructose (found in fruit, honey, and many sweetened drinks) and a group of carbohydrates collectively called FODMAPs, which include certain grains, vegetables, and artificial sweeteners.
Gluten sensitivity is another possibility. Even in people who don’t have celiac disease, gluten can alter the gut’s barrier function and trigger symptoms that overlap heavily with irritable bowel syndrome, including pain, bloating, and changes in bowel habits. An elimination diet, where you remove suspect foods for a few weeks and reintroduce them one at a time, is often the most practical way to identify the trigger.
Fiber plays a role too. The recommended daily intake is 25 to 38 grams depending on your age and sex, but most people fall short. Ironically, both too little fiber and a sudden spike in fiber intake can cause stomach pain. Adding high-fiber foods too quickly gives your gut bacteria more to ferment than they’re prepared for, producing excess gas, bloating, and cramping. Increasing fiber gradually over a few weeks lets your digestive system adjust.
Where It Hurts Matters
Your abdomen contains organs from multiple systems packed into a relatively small space, and the location of your pain is one of the strongest clues to its source.
Upper right side: This is where your gallbladder and liver sit. Pain here, especially after a fatty meal, often points to gallstones or gallbladder inflammation. Kidney stones or infections on the right side can also radiate to this area.
Upper left side: Stomach ulcers, gastritis (inflammation of the stomach lining), and pancreatitis tend to produce pain here or in the upper middle area. Pancreatitis pain is often severe and can radiate to the back.
Lower right side: This is the classic location for appendicitis. The pain typically starts vague and diffuse around the belly button, then migrates to the lower right over several hours. That migration pattern is one of the most reliable signs, with about 80% accuracy for identifying appendicitis.
Lower left side: Diverticulitis, an infection of small pouches that form in the colon wall, is a common cause of pain in this area, particularly in adults over 40.
Lower abdomen generally: Bladder issues, hernias, inflammatory bowel disease, and reproductive organ problems can all produce pain in the lower belly.
Medications That Irritate the Gut
Anti-inflammatory painkillers like ibuprofen and aspirin are among the most frequent medication-related causes of stomach pain. They work by blocking chemicals called prostaglandins that drive inflammation, but those same chemicals also help protect your stomach lining. Without that protection, the lining becomes more vulnerable to acid damage, which can cause anything from mild discomfort to full-blown ulcers with prolonged use.
Antibiotics commonly trigger stomach upset by disrupting the balance of bacteria in your gut. The disruption can cause cramping, diarrhea, and nausea that typically resolve once you finish the course. Metformin, one of the most widely prescribed diabetes medications, is also well known for gastrointestinal side effects including nausea, bloating, diarrhea, and abdominal pain, particularly when first starting it.
Stress and the Gut-Brain Connection
Your digestive tract has its own nervous system, sometimes called the “second brain,” containing the same types of neurons and signaling chemicals found in your actual brain. This gut-brain connection is why anxiety, chronic stress, and emotional upheaval can cause very real stomach pain, not imagined pain.
When you’re stressed enough to trigger a fight-or-flight response, digestion slows or stops entirely so your body can redirect energy toward the perceived threat. Even milder stress, like giving a presentation or dealing with a difficult situation at work, can temporarily disrupt digestion and cause cramping, nausea, or a churning feeling. Serotonin, a chemical most people associate with mood, is actually produced in large quantities in the gut and plays a key role in this two-way communication. For people with irritable bowel syndrome, this connection is amplified: the gut becomes hypersensitive to normal digestive activity, interpreting ordinary signals as pain.
Chronic Conditions Behind Recurring Pain
If your stomach aches keep coming back over weeks or months, a chronic condition may be responsible. Irritable bowel syndrome (IBS) is one of the most common. It’s diagnosed when you’ve had abdominal pain for at least 12 weeks over a year, along with changes in how often you go to the bathroom or changes in the consistency of your stool. IBS doesn’t damage the intestines, but it can significantly affect quality of life.
Inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis, is a different category entirely. Unlike IBS, IBD involves actual inflammation and damage to the digestive tract, and it requires medical treatment to manage. The symptoms can overlap with IBS (pain, diarrhea, urgency), but IBD often also causes weight loss, bloody stool, and fatigue.
Stomach ulcers and chronic gastritis are other repeat offenders. These involve damage or inflammation to the stomach lining, often caused by a bacterial infection (H. pylori) or long-term use of anti-inflammatory painkillers. The pain tends to be a burning or gnawing sensation in the upper abdomen that may improve or worsen with eating, depending on the location of the ulcer.
Reproductive Organ Causes in Women
Lower abdominal pain in women isn’t always a digestive issue. Pelvic inflammatory disease and complications from ovarian cysts are the most common gynecological causes of non-pregnancy-related abdominal pain. Pelvic inflammatory disease, usually caused by sexually transmitted bacteria, typically produces bilateral lower abdominal pain along with abnormal vaginal bleeding or discharge.
Ovarian cysts tend to cause one-sided pain, sometimes radiating to the lower back, that can be gradual or sudden if a cyst ruptures. Endometriosis, which affects an estimated 10 to 15 percent of women of reproductive age, causes inflammation and pain due to tissue similar to the uterine lining growing outside the uterus. The pain often follows a cyclical pattern tied to the menstrual cycle. An ectopic pregnancy, where a fertilized egg implants outside the uterus, causes severe abdominal pain and vaginal bleeding and is a medical emergency.
Signs That Need Immediate Attention
Most stomach aches are not emergencies, but certain patterns warrant a trip to the emergency room. Seek immediate care if the pain is sudden and severe, or if it doesn’t ease within 30 minutes. Continuous severe pain accompanied by nonstop vomiting may indicate a serious or life-threatening condition.
- Appendicitis: Pain that starts around the belly button and moves to the lower right abdomen, often with loss of appetite, nausea, vomiting, or fever.
- Acute pancreatitis: Severe pain in the upper middle abdomen that may last for days, sometimes worsening after eating, with nausea, fever, and a rapid pulse.
- Ectopic pregnancy: Severe abdominal pain with vaginal bleeding in someone who could be pregnant.
- Bowel obstruction: Intense cramping with inability to pass gas or have a bowel movement, often with vomiting.
Blood in your vomit or stool, a rigid abdomen that’s painful to touch, high fever alongside abdominal pain, or pain following an abdominal injury are all reasons to get evaluated right away rather than waiting it out.