GERD typically occurs when the lower esophageal sphincter, which is a muscle at the end of the esophagus, relaxes inappropriately. This allows acid from the stomach to come up into the esophagus fairly frequently. This then causes inflammation of the end of the esophagus, and this can progress on to ulceration, which is the more severe type of inflammation, and scarring, which can lead to what is called a stricture.