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How does gastroesophageal reflux disease cause heartburn?

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Why do people feel full after a big meal? — digestive system disease Learn why eating large meals can cause bloating, heartburn, and discomfort.

Gastroesophageal reflux disease (GERD) causes heartburn when gastric contents—including stomach acid and digestive enzymes—frequently flow backward from the stomach into the esophagus.12

This reflux occurs due to the inadequate functioning of anti-reflux mechanisms, most notably the lower esophageal sphincter, which normally acts as a barrier to keep stomach contents below the diaphragm. When this muscle relaxes inappropriately or fails to maintain proper tension, acidic material enters the esophagus. Because the esophageal lining is not designed to withstand these harsh digestive fluids, the contact leads to chemical inflammation and a characteristic burning sensation behind the sternum known as heartburn.231

Factors such as obesity, hiatal hernia, or pregnancy can increase intra-abdominal pressure or distort the anatomy, further impairing the sphincter's ability to prevent this reflux. If the esophagus cannot clear the refluxed material efficiently, the persistent exposure to acid can lead to more severe complications, including peptic ulceration and Barrett esophagus.12