Reflux occurs when the contents of the stomach back up into the esophagus, the tube that connects the mouth to the stomach. In some cases, this food and stomach acid also backs up into the mouth. Most infants experience episodes of reflux during the first three months of life. This is evident when babies “burp up.”

Many children also experience occasional bouts of reflux. In rare cases, older children may experience more persistent reflux. Up to 7 million children and teenagers in the United States – one out of every 10 – experience occasional problems with reflux, according to the Pediatric Adolescent Gastroesophageal Reflux Association (PAGER).

The esophagus carries food from the mouth to the stomach. The lower esophageal sphincter (LES) is a group of muscles that serves as a valve between the esophagus and stomach. When food reaches the LES, the LES relaxes and allows the food to enter the stomach. After food enters the stomach, the LES contracts to prevent food and other stomach contents from backing up into the esophagus. The sphincter also opens to release gas during burping after meals.

Reflux occurs when the LES, which separates the esophagus and stomach, does not close properly and/or is weak. The majority of reflux episodes are associated with transient lower esophageal relaxation (tLESR), in which the LES relaxes momentarily, allowing gas in the stomach to vent. This occurs in most people from time to time, particularly when the stomach is distended. Unexpected burping is an example of tLESR.

Hiatal hernia is also a well-known cause for acid reflux. However, reflux in infants often occurs because the LES is not yet fully developed, or the gastrointestinal tract is not yet fully coordinated. When the LES is weakened or remains relaxed for too long, contents of the stomach can reflux into the esophagus. The tissue lining the esophagus differs from the stomach lining and is more susceptible to acid. This causes a burning sensation in the chest or throat called heartburn.

In other cases, stomach contents may be refluxed all the way up into the mouth before they are swallowed again. When gastric acid can be tasted in the back of the mouth, it is called acid indigestion. In some people, reflux affects the vocal cords or causes stomach contents to flow into the lungs (aspiration).

Almost everybody experiences occasional reflux, even if they are not aware of it. This is normal, and episodes usually clear up on their own. Reflux may occur immediately after eating or may not appear for several hours afterward. Infants are particularly likely to experience repeated episodes of reflux, which usually fade after a child turns 1 or 2 years old. However, in some cases reflux may indicate a more serious problem.

Left untreated, reflux problems can have a significant impact on a child’s physical and emotional health. Some babies with reflux may withdraw from the world and develop unhealthy attitudes about eating, including a fear of foods. Persistent reflux can damage the lining of the esophagus. This is known as gastroesophageal reflux disease (GERD).

Some children may develop other significant health problems, feeding and nutrition problems (including poor weight gain) or breathing difficulties. Persistent reflux that continues after infancy and into childhood may also indicate a health problem.