Backflow of stomach acid into the esophagus. Acid reflux frequently happens when the lower esophageal sphincter (LES) relaxes more often than it should and/or at inappropriate times. This allows harsh stomach juices to back up into the esophagus.
A condition in which acid flows back up from the stomach into the upper intestines and the esophagus.
Acid reflux is when stomach acid flows back up into the food pipe. The primary symptom of acid reflux is heartburn.