When a person eats, food passes from the throat to the stomach through the esophagus. The esophagus is called the food pipe or swallowing tube.
A ring of muscle fibers prevents food at the top of the stomach prevents food from moving up into the esophagus. These muscle fibers are called the lower esophageal sphincter, or LES. If this muscle doesn't close well, food can leak back into the esophagus. This is called gastroesophageal reflux (GERD).
A small amount of gastroesophageal reflux is normal young infants. However, ongoing reflux with frequent vomiting can irritate the esophagus and make the infant fussy. Severe reflux that causes weight loss or breathing problems is not normal.