Pronounced – LOH-wur uh-saw-fuh-JEE-ul SFEENK-tur

The lower esophageal sphincter (LES) is a ring of muscle between the esophagus and stomach that opens and closes to allow food to enter the stomach.

When a person swallows, the lower esophageal sphincter muscle relaxes to let food pass from the esophagus to the stomach. The lower esophageal sphincter stays closed at other times to keep stomach contents from flowing back into the esophagus. Reflux can occur when the LES opens, allowing stomach contents and acid to come back up into the esophagus.

The lower esophageal sphincter normally opens to release gas after meals. With infants, when the lower esophageal sphincter opens, stomach contents often reflux into the esophagus and out the mouth, resulting in regurgitation, or spitting up, and vomiting.