Gastroesophageal reflux disease results when the lower esophageal sphincter—the muscle that acts as a valve between the esophagus and stomach—becomes weak or relaxes when it should not, causing stomach contents to rise up into the esophagus.
Abnormalities in the body such as hiatal hernias may also cause GERD. Hiatal hernias occur when the upper part of the stomach moves up into the chest. The stomach can slip through an opening found in the diaphragm. The diaphragm is the muscle wall that separates the stomach from the chest. Hiatal hernias may cause GERD because of stomach acid flowing back up through the opening; however, most produce no symptoms.
Other factors that can contribute to GERD include
obesity
pregnancy
certain medications, such as asthma medications, calcium channel blockers, and many antihistamines, pain killers, sedatives, and antidepressants
smoking, or inhaling secondhand smoke
People of all ages can develop GERD, some for unknown reasons.