Gastroesophageal reflux disease (GERD) is a common condition in which the stomach contents move up into the esophagus.
Reflux may damage the esophagus, pharynx or respiratory tract.
Lower esophageal sphincter (LES) relaxes to allow food and liquid to flow into stomach and closes to stop acid from moving back to esophagus. If Lower esophageal sphincter (LES) relaxes abnormally or weakens, stomach acid can flow back up into esophagus. https://www.carehospitals.com/animated-detail/gerd-gastroesophageal-reflux-disease-gerd-causes-symptoms-treatment