Causes

In infants, the ring of muscle between the esophagus and the stomach — the lower esophageal sphincter (LES) — is not yet fully mature. That allows stomach contents to flow back up. Eventually, the LES will open only when your baby swallows and will remain tightly closed at other times, keeping stomach contents where they belong.

The factors that contribute to infant reflux are common in babies and often can't be avoided. These factors include:

• Lying flat most of the time
• Consuming an almost completely liquid diet
• Being born prematurely

Occasionally, infant reflux can be caused by more-serious conditions, such as:

• GERD. The reflux has enough acid to irritate and damage the lining of the esophagus.
• Pyloric stenosis. A valve between the stomach and the small intestine is narrowed, preventing stomach contents from emptying into the small intestine.
• Food intolerance. A protein in cow's milk is the most common trigger.
• Eosinophilic esophagitis. A certain type of white blood cell (eosinophil) builds up and injures the lining of the esophagus.
• Sandifer syndrome. This causes abnormal tilting and rotation of the head and movements that resemble seizures. It's a rarely seen consequence of GERD.