The stomach contents regurgitate and back up (reflux) into the esophagus The food in the stomach is partially digested by stomach acid and enzymes. Normally, the partially digested acid content in the stomach is delivered by the stomach muscle down into the small intestine for further digestion. With esophageal reflux, stomach acid content refluxes [..]

a condition in which infants may spit up a mixture of gastric acid and breast milk/formula because the sphincter between the esophagus and stomach is weak