Why acid reflux occurs
Stomach acid, which we need to digest our food, is not a problem when it stays where
it belongs—in your stomach.
Acid reflux is a physical condition where the contents of the stomach—including
acid—back up (or reflux) into the esophagus (the tube that carries food from your
mouth to your stomach). If this condition happens too frequently, it could cause acid reflux disease.
The role of the LES
Between your esophagus and your stomach there is a natural barrier, or valve, called
the lower esophageal sphincter (LES). For most people, the LES
works just fine. But for some people with acid reflux disease, this valve does not
always work the way it should for 2 reasons:

Damage to the esophagus
The lining of your stomach is built to handle stomach acid. But the lining of your
esophagus is not. It can protect itself for a while, but when acid comes in contact
with this lining for an extended period of time, it can lead to serious damage.
And as a result, you may experience heartburn and other painful or uncomfortable
symptoms.
If left untreated, acid reflux disease may even cause damage (erosions) to the lining
of the esophagus, a condition known as erosive esophagitis. If
you have any concerns about your symptoms, please be sure to talk to your doctor.
Next: What happens?