Lower Esophageal Sphincter (LES) Dysfunction and Acid Reflux: Causes and Mechanisms

The lower esophageal sphincter (LES) is the muscular valve separating the stomach from the esophagus. It allows food to pass into the stomach but prevents reflux of stomach contents back into the esophagus.

When the LES relaxes inappropriately or becomes weak, it permits stomach acid and other contents to flow back into the esophagus, causing symptoms of acid reflux disease such as heartburn and regurgitation.