Acid reflux is commonly called Gastroesophageal Reflux Disease. It is the spilling of the stomach contents, (food, acid, pepsin, bile acids, and pancreatic enzymes) into the esophagus. A small amount of spilling of stomach contents happens in all individuals, especially after meals. Only when symptoms and complications occur is it considered a problem.

When the esophagus is exposed to the acidic stomach content repeatedly and for long periods of time inflammation of the esophagus occurs (reflux esophagitis) and this can progress to erosion of the esophagus (erosive esophagitis). Interestingly, acid reflux is not generally caused by too much acid in the stomach but by the acid remaining too long in the esophagus.