<p class="MsoNormal"><span style="mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;
color:rgb(0,0,0);font-size:16.0000pt;mso-font-kerning:1.0000pt;">It occurs when the muscle between the stomach and oesophagus (the lower oesophageal sphincter) relaxes too often, allowing acid to rise upwards.</span></p>