Acid reflux is a common condition in which the contents of the stomach rise backward (reflux) into the esophagus--the muscular tube that connects the throat and stomach. It is more specifically referred to as gastroesophageal reflux disease (GERD). There are a number of reasons why acid reflux is painful.
There is a ring of muscle between the esophagus and the stomach called the lower esophageal sphincter (LES). The LES works as a valve mechanism that opens to let food and fluid pass into the stomach and then closes tightly to prevent a backflow into the esophagus. When the LES fails to stay closed, the stomach contents may back up into the esophagus, causing acid reflux. It may open spontaneously for varying lengths of time or may fail to not close properly, allowing stomach contents to rise into the esophagus.
The refluxed stomach contents have a corrosive, inflammatory effect on the delicate lining of the esophagus, causing a number of painful symptoms. This is because your stomach contains gastric acids, including hydrochloric acid, which it secretes to help digest the food you eat. However, while the stomach walls are adapted to handle constant exposure to its highly acidic contents, the esophagus is not. As a result, the refluxed stomach acids cause painful symptoms when they come into contact with the inner esophagus.
The most common symptom of acid reflux is heartburn, a burning sensation of pain in the upper abdomen that may radiate upward into the throat. Also called acid indigestion, heartburn may be accompanied by a burning pain in the pit of the stomach, just below the breastbone.
Left untreated, acid reflux can cause a number of painful complications such as dysphagia, or painful, difficult swallowing. Continued exposure to the refluxed stomach acids tends to result in scarring of the esophageal tissues. Over time, this results a stricture or narrowing of the lower esophagus that may cause dysphagia. It may also cause painful ulcers to form.
Acid reflux may sometimes cause a severe chest pain just behind the breastbone that mimics and may be mistaken for a heart attack. The Mayo Clinic recommends getting immediate emergency help if the pain is accompanied by nausea, dizziness, sweating or a shortness of breath, or if the pain radiates into your neck, arm and shoulder.