Ranked causes (most to least common)

• This is the most common cause of troublesome, repetitive belching. Sleisenger and Fordtran's says "chronic eructation is almost always a behavioral disorder."
• In supragastric belching, air is sucked or injected into the esophagus from the pharynx and expelled at once. It usually never reaches the stomach.
• It is often triggered by emotional stress and typically occurs after meals.
• Patients often have underlying postprandial dyspeptic symptoms that they misread as "gas." Belching gives brief relief, which reinforces the habit.
• Aerophagia is true excess air swallowing. It is a separate entity: the main complaints are bloating and distension, and belching is secondary. Triggers include gulping food, chewing gum, smoking, carbonated drinks and anxiety (Harrison's, 22nd ed.).
• Associated conditions include anxiety, obsessive-compulsive disorder and bulimia nervosa.

• Belching and reflux have a bidirectional relationship. Belching can trigger reflux, and heartburn may drive compensatory air swallowing.
• About 40% of patients with excessive supragastric belching have pathologic acid exposure, and about 95% have typical reflux symptoms (from a supragastric belching review).
• Supragastric belching appeared in about 35% of PPI-refractory GERD patients in one cohort.
• Consider this cause when belching comes with heartburn or regurgitation, or persists despite a PPI.

• Belching is a common symptom in these patients. It is often the "excess gas" complaint that underlies the postprandial discomfort described above.

• These include eating fast, large meals, carbonated drinks, chewing gum, smoking, and ill-fitting dentures. They are very common but are usually transient, so they tend not to bring patients to clinic.

• Gastric distension from overeating, aerophagia or delayed emptying stresses the gastroesophageal junction and promotes belching and reflux (Mulholland and Greenfield's Surgery, 7th ed.).

• These are classic textbook associations. I did not find good data on how often they cause isolated belching, so treat the rank as uncertain.

• This is common after total fundoplication, where belching is hard in the first few months (Fischer's Mastery of Surgery, 8th ed.). It is only relevant to patients who have had that surgery.

• Examples are lactose or fructose intolerance, FODMAP intolerance, celiac disease and small intestinal bacterial overgrowth. They mostly cause bloating and flatus, with belching a secondary complaint.

• Examples are tardive dyskinesia, where respiratory dyskinesia can cause aerophagia and belching (Kaplan and Sadock's), and GLP-1 agonists or metformin, though I did not verify the latter two against a source.

• Examples are gastric outlet obstruction, gastric or esophageal malignancy, hiatal hernia and biliary disease. Belching is almost never the only symptom here.

Practical points

• Red flags: dysphagia, weight loss, vomiting, GI bleeding, anemia, or onset after age 50 to 60. These warrant endoscopy and a workup for organic disease.
• Isolated belching without red flags: this is usually behavioral. The textbook advises reserving radiologic and endoscopic evaluation for patients with other suggestive symptoms or signs.
• Diagnosis of supragastric belching: pH-impedance monitoring or high-resolution impedance manometry is the gold standard. More than 13 supragastric belches per 24 hours is considered abnormal.
• Treatment of supragastric belching: speech therapy or behavioral therapy, including diaphragmatic breathing. Treat any coexisting GERD or dyspepsia.

Evidence check