Immature Lower Esophageal Sphincter
The lower esophageal sphincter (LES) is a ring of muscle at the bottom of the esophagus that opens to allow food into the stomach and closes to keep it there. This muscle isn't fully matured in infants. When the LES opens, the contents of the stomach can flow back into the esophagus, causing the infant to spit up or vomit. Constant regurgitation from acid reflux can cause damage to the esophageal lining.
Short or Narrow Esophagus
Refluxed stomach contents have a shorter distance to travel if the esophagus is shorter than normal. Refluxed stomach contents can irritate the lining if the esophagus is narrower than normal.
Certain foods may be causing acid reflux, depending on your infant's age. For example, citrus fruits and tomato products increase acid production in the stomach. Foods like chocolate, peppermint, and high-fat foods can keep the LES open longer, causing the contents of the stomach to reflux.
Changing the foods your infant eats can help reduce the chances of acid reflux. Changing your diet can help reduce acid reflux if you breastfeed.
Gastroparesis (Delayed Emptying of the Stomach)
Gastroparesis is a disorder that causes the stomach to take too long to empty. The stomach normally contracts to move food down into the small intestine for digestion. However, stomach muscles don’t work properly if there is damage to the vagus nerve, which controls the movement of food from the stomach through the digestive tract. This causes the stomach contents to remain in the stomach longer than they’re supposed to, encouraging reflux.
A hiatal hernia is a condition in which part of the stomach sticks through an opening in the diaphragm. A small hiatal hernia doesn’t cause problems, but a larger one can cause acid reflux and heartburn.
Hiatal hernias are very common, especially in people over the age of 50. However, the causes are unknown. A hiatal hernia in children is usually congenital and causes gastric acid to reflux from the stomach into esophagus.
Positioning—especially during and after feeding—is a frequently overlooked cause of acid reflux in infants. A horizontal position makes it easier for the stomach contents to reflux into the esophagus. Simply keeping your infant in an upright position while you’re feeding them and for 20 and 30 minutes afterwards can reduce acid reflux.
This also applies to sleeping positions. It’s recommended that babies sleep on their backs to prevent sudden infant death syndrome (SIDS). However, babies who experience reflux may benefit from sleeping in a slightly elevated position on their left sides. This position makes it harder for the stomach contents to reflux.
Angle of His
The angle at which the base of the esophagus joins the stomach is known as the “angle of His” and can cause acid reflux. The exact function of the angle is unknown. However, it most likely works together with the LES to keep the contents of the stomach from refluxing. If the angle is too sharp or too steep, it may make it difficult to keep the stomach contents down.
Feeding your infant too much at once, either with a bottle or while breastfeeding, can cause acid reflux. Feeding your infant too frequently can also cause acid reflux. An oversupply of food can put too much pressure on the LES, which will cause your infant to spit up. That unnecessary pressure is taken off the LES and reflux decreases when you feed your infant less food more often.
While it isn’t easy to determine the exact cause of acid reflux in infants, lifestyle and diet changes may help eliminate some of the leading factors. If the acid reflux doesn’t go away with these changes, a doctor may have to perform tests to rule out a gastrointestinal obstruction or other problems with the esophagus.