Stress, h. pylori infection, or hiatal hernia can cause lower esophageal sphincter dysfunction leading to reflux.

“Now you have a sphincter down here at the bottom of the esophagus. Okay, this is called your ales. This is your lower esophageal sphincter. Now typically this sphincter is supposed to open up like a gate. [...] Now when you have excessive stress, when you have H pylori, when you have potentially a hyal hernia, all of a sudden this is not working properly, the valves getting stuck open, then you have this reflux disease.”