Stomach problems fall into a surprisingly short list of common causes, and where your pain sits, when it strikes, and what other symptoms come with it can narrow things down fast. Most stomach complaints trace back to acid irritation, infection, food intolerance, or a functional issue like irritable bowel syndrome. Here’s how to sort through the possibilities.
Where the Pain Is Matters
Your abdomen contains dozens of organs packed into a relatively small space, and the location of your discomfort is one of the strongest clues to its source. Pain in the upper middle area, just below the breastbone, points toward the stomach itself or the first stretch of the small intestine. A burning or gnawing feeling there, especially after eating, is the hallmark of indigestion, gastritis, or an ulcer.
Upper right pain is more likely tied to your gallbladder or liver. Upper left pain can signal a problem with the spleen or the tail of the pancreas. Lower abdominal pain shifts attention to the intestines, the bladder, or reproductive organs. If the pain is generalized and hard to pin down, that’s common with gas, bloating, constipation, or a stomach bug. A sudden, severe pain that stays in one spot, especially the lower right, warrants immediate attention because it could indicate appendicitis.
Gastritis and Stomach Lining Irritation
Gastritis is one of the most common reasons your stomach feels off. It’s inflammation of the mucus-lined barrier that protects your stomach wall from its own digestive acid. When that barrier weakens, acid contacts the tissue underneath and causes a burning or aching pain in the upper belly, nausea, and a heavy fullness after meals.
The three biggest triggers are a bacterial infection called H. pylori, regular use of common painkillers like ibuprofen and naproxen, and heavy alcohol use. Over-the-counter anti-inflammatory drugs are a particularly sneaky cause because people take them routinely without realizing they’re eroding the stomach lining. The risk also increases with age, because the protective lining naturally thins over time. Gastritis can be short-lived (a rough weekend of drinking, for instance) or chronic, simmering for weeks or months.
Ulcers and H. Pylori Infection
If gastritis goes unchecked, or if H. pylori infection persists, the damage can deepen into a peptic ulcer, an actual sore in the stomach lining or the upper small intestine. Historically, about 85% of stomach ulcers and 95% of duodenal ulcers have been linked to H. pylori, and people carrying the bacterium are 3 to 10 times more likely to develop an ulcer than those without it.
Ulcer pain tends to be more focused and intense than general indigestion. It often improves briefly after eating, then returns. Some people wake up with pain in the middle of the night. H. pylori is treatable with a course of antibiotics combined with acid-reducing medication, and most ulcers heal within a few weeks once the infection is cleared and the irritant is removed.
Acid Reflux and Functional Dyspepsia
Acid reflux, or GERD, happens when stomach acid flows back into the esophagus, causing heartburn, chest tightness, and sometimes a sour taste in the mouth. Functional dyspepsia is a closely related condition where you feel persistent upper stomach pain, early fullness, or bloating, but tests don’t reveal an ulcer or structural problem. The two conditions overlap frequently because they share underlying mechanics: the stomach empties too slowly, or it doesn’t expand properly when food arrives.
People who have both conditions together tend to have a noticeably heavier symptom burden and end up at the doctor’s office more often than those with either condition alone. A specific pattern called postprandial distress syndrome, where the discomfort hits primarily after meals, is especially common in people dealing with this overlap. If you feel painfully full after small meals and also get heartburn, both issues may be in play.
Stomach Bugs and Food Poisoning
A sudden onset of nausea, vomiting, cramping, and diarrhea usually points to an infection. Viral gastroenteritis, often called the stomach flu, typically shows up 1 to 3 days after exposure and lasts a day or two, though it can drag on for up to 14 days. Bacterial food poisoning from organisms like salmonella or E. coli can look nearly identical, which is why it’s easy to confuse the two.
The key differences come down to timing and severity. Food poisoning from bacteria often hits faster (sometimes within hours of eating contaminated food) and is more likely to cause fever and bloody stool. Viral stomach bugs spread through close contact and tend to move through households one person at a time. Both usually resolve on their own with rest and fluids, but bloody stool, high fever, or an inability to keep liquids down for more than a day signals something more serious.
Food Intolerances
If your stomach problems come and go and seem connected to specific meals, a food intolerance could be the cause. Lactose intolerance (difficulty digesting dairy sugar) and fructose intolerance (difficulty absorbing fruit sugar) are the most common culprits. In both cases, undigested sugars reach the large intestine and get fermented by gut bacteria, producing gas, bloating, cramping, and diarrhea.
What makes intolerances tricky is that symptoms don’t always match the degree of malabsorption. Some people absorb these sugars poorly on a breath test but feel fine, while others test normal but experience significant discomfort. The symptom pattern matters more than the test result. Diarrhea is more common than constipation in people with confirmed lactose or fructose malabsorption, so if your stomach trouble consistently pairs with loose stools after dairy, fruit, or foods sweetened with high-fructose corn syrup, an intolerance is worth exploring. An elimination diet, where you remove the suspect food for two to three weeks and reintroduce it, is the simplest way to test this at home.
Irritable Bowel Syndrome
IBS is diagnosed when you have recurring abdominal pain tied to bowel movements, along with a change in how often you go or what your stool looks like, and no other condition explains it. The pain needs to have been present at least one day per week for the past three months to meet the diagnostic threshold. IBS is a “functional” disorder, meaning the gut looks structurally normal but doesn’t behave normally.
There are three subtypes: one dominated by diarrhea, one by constipation, and one that alternates between the two. Stress, certain foods, hormonal shifts, and disrupted sleep are well-known triggers. IBS doesn’t damage the intestine or lead to more serious disease, but it can significantly affect quality of life. Management typically involves identifying personal triggers, adjusting fiber intake, and in some cases using medications that target gut motility or sensitivity.
Bacterial Overgrowth in the Small Intestine
Small intestinal bacterial overgrowth, or SIBO, occurs when bacteria that normally live in the large intestine colonize the small intestine in excessive numbers. This causes bloating, gas, abdominal pain, and diarrhea that can look a lot like IBS. In fact, a meaningful percentage of people diagnosed with IBS turn out to have SIBO as a contributing factor.
SIBO is diagnosed with a breath test. You drink a sugar solution, then breathe into a collection device at intervals. A rise in hydrogen gas of 20 parts per million or more above baseline within 90 minutes is considered positive. A methane level of 10 parts per million or more at any point during the test also counts. Elevated methane is more associated with constipation, while hydrogen-dominant overgrowth tends to cause diarrhea. Treatment involves targeted antibiotics and sometimes dietary changes to prevent recurrence.
When Stomach Pain Is an Emergency
Most stomach problems are uncomfortable but not dangerous. However, certain symptoms indicate something that needs immediate medical attention:
- Vomiting blood or material that looks like coffee grounds
- Black or bloody stool
- A swollen, rigid, tender abdomen
- Severe pain following an accident or injury
- Stomach pain accompanied by chest pain, shortness of breath, or dizziness
- High fever with abdominal pain
- Persistent vomiting that prevents you from keeping any fluids down
These can signal internal bleeding, a perforation, a bowel obstruction, or another condition that worsens quickly without treatment.
What Testing Looks Like
If your symptoms persist or are severe enough to investigate, your doctor will likely start with a physical exam and blood work. From there, the next step depends on what they suspect. Standard imaging includes ultrasound, CT scans, and X-rays, sometimes paired with a barium swallow (you drink a chalky liquid that makes your digestive tract visible on imaging).
For a closer look, an upper endoscopy uses a thin, flexible tube with a camera threaded through the mouth into the stomach and upper intestine. This lets the doctor see inflammation, ulcers, or abnormal tissue directly, and take small tissue samples if needed. The procedure is done under sedation and typically takes 15 to 30 minutes. A breath test can check for H. pylori infection, SIBO, or sugar malabsorption without any invasive procedure at all. Which tests you need depends on your specific symptoms, how long they’ve lasted, and whether initial treatments have helped.