The stomach produces an acid which is mixed in the food eaten. The acid is not of importance but it gets mixed anyway as the food is digested and travels from the stomach to the intestines. However, there are instances when this acid goes up to the esophagus which is not normal. The lower end of the esophagus called the sphincter tends to lose its firmness, which allows the stomach acid to move up to the esophagus. When this happens, the medical field termed it as an acid reflux.