Relux is where some of the contents of your stomach (either acid juices, bile or undigested food) intermittently pass back up into your oesophagus in your chest (food pipe), rather than staying blow your diaphragm in your abdomen and only passing through your bowel. This can occur with a structurally normal stomach anatomy (and just a weak ‘anti-reflux valve’) or when there is a hiatus hernia (where the stomach has partially moved up into your chest). A hiatus hernia can also be present without causing reflux (either no symptoms, or other symptoms like troubles swallowing or chest pain)