Acid is produced naturally in your stomach to help you digest food and to kill bacteria. This acid is irritant so your body produces a natural mucous barrier which protects the lining of your stomach. In some people, this barrier can break down allowing the acid to damage the stomach, causing inflammation, ulcers and other conditions. Other people can have a problem with the muscular band at the top of the stomach that keeps the stomach tightly closed. This may allow the acid to escape and irritate the oesophagus, causing heartburn. This is often referred to as 'acid reflux'.
This is a companion discussion topic for the original article at https://patient.info/medicine/lansoprazole-to-reduce-stomach-acid-zoton-fastab-prevacid