What causes acid reflux from the stomach?

Gastroesophageal reflux—commonly referred to as “acid regurgitation”—occurs when gastric contents flow backward from the stomach into the esophagus and up to the oropharynx, resulting in a sour or acidic taste in the mouth. Acid reflux commonly occurs after meals and during nighttime, often accompanied by a burning sensation behind the sternum—commonly known as “heartburn.”

The underlying causes fall into two main categories: pathological factors and dietary influences. Pathological causes include gastric disorders triggered by excessive gastric acid secretion, which irritates the gastric mucosa and leads to heartburn and acid regurgitation. Examples include gastritis, peptic ulcer disease, gastroesophageal reflux disease (GERD), and functional dyspepsia. Additionally, certain medications—particularly nonsteroidal anti-inflammatory drugs (NSAIDs) and antipyretic-analgesics—can damage the gastric mucosa and provoke acid reflux and heartburn. As GERD worsens, patients may experience retrosternal pain, which can sometimes be mistaken for cardiac chest pain; prompt medical evaluation is therefore essential to ensure accurate diagnosis and appropriate management.

The second category comprises dietary and lifestyle factors. For instance, overeating or consuming large, heavy meals increases intragastric pressure. When lying down, gravity further facilitates the reflux of gastric contents into the esophagus—and subsequently into the oral cavity—causing acid regurgitation and heartburn.

We recommend that affected individuals avoid overeating and instead maintain moderate portion sizes—ideally eating until about 70–80% full. They should also refrain from lying down immediately after meals and avoid late-night dinners. Furthermore, smoking cessation is strongly advised, as nicotine impairs lower esophageal sphincter function, promoting reflux and worsening symptoms.