Dr. Greene's Answer
Normally, when someone swallows, the food travels down the esophagus, a sphincter at the lower end relaxes, and the food is permitted to enter the stomach, where a pool of acid awaits to continue digesting it. The sphincter then closes tight. Not so in gastroesophageal reflux.
When the sphincter does not remain tightly closed, the acid and the food slosh back up into the esophagus. This is what is meant by reflux. These refluxed stomach contents can burn the lining of the esophagus and irritate the lungs. A small amount of reflux immediately following meals is common in healthy adults and causes no problems. Swallowing saliva to wash away the acid protects the vulnerable walls of the esophagus.
In most newborns, the lower esophageal sphincter is relatively lax. Thus, frequent spitting up is common in infants. This is called physiologic reflux. Over time, the lower esophageal sphincter becomes more competent; children eat more solid food; they assume a more upright posture. The spitting up diminishes. In most cases the spitting up resolves without treatment by about 18 months of age. If reflux persists beyond age 2, there is generally not much improvement until at least age 4. Over the next few years, a number of children outgrow the condition, but the closer they get to puberty with reflux, the more likely they are to have reflux as adults — unless corrected.
When reflux lasts beyond about 18 months, or when it is associated with other symptoms at any age, it should be evaluated. These other symptoms might include poor weight gain, heartburn, irritability (especially after eating or while lying down), bad breath, excessive cavities, wheezing, chronic cough, pain with eating, or recurrent pneumonias. A child might have any or all of these symptoms, but not actually spit up, if the stomach contents are re-swallowed.