The primary cause of acid reflux is the moving of stomach acid into the esophagus, according to WebMD. Typically, the lower esophageal sphincter closes off the entrance of the stomach, but failure of the sphincter to close completely can allow acid to escape into the esophagus.
If an individual experiences symptoms of acid reflux more than two times a week, it is likely he has acid reflux disease, as noted by WebMD. A stomach abnormality called hiatal hernia, a result of the upper portion of the stomach and sphincter moving above the diaphragm, can result in increased levels of acid reflux. Other risk factors include pregnancy, smoking, obesity and ingesting certain foods and beverages.