Acid reflux is a common medical condition in which acid from the stomach flows back into the esophagus. It is also called gastroesophageal reflux. Symptoms include heartburn, chest pain, gas, and vomiting. Prolonged acid reflux can cause inflammation of the esophagus. In a few cases, such inflammation can in turn lead to ulcerations, scarring, and even cancer of the esophagus. When acid reflux damages the esophagus, the condition is called gastroesophageal reflux disease (GERD).