Gastroesophageal reflux disease (GERD) develops when stomach acid and juices back up, or reflux, into the esophagus, the muscular tube that connects the throat to the stomach. This happens when the valve between the lower end of the esophagus and the stomach (the lower esophageal sphincter) does not close tightly enough.

See a picture of how reflux happens.

GERD most commonly occurs when the lower esophageal sphincter relaxes at the wrong time (that is, when you are not swallowing) and remains open too long. Normally, the valve opens for only a few seconds when you swallow. But certain foods may relax the valve so that it does not close as tightly, making reflux more likely. These foods include chocolate, onions, peppermint, coffee, high-sugar foods, and possibly high-fat foods. Alcohol, tobacco (nicotine), and some medicines can also relax the lower esophageal sphincter.

Other foods, though they do not relax the valve, may cause heartburn if the esophagus is already irritated. These foods include spicy foods, citrus products, and tomato products.

Other factors can allow stomach juices to back up into the esophagus, such as:

• Hormonal changes during pregnancy. The valve may not close as tightly during pregnancy because of hormonal changes and increased abdominal pressure. Heartburn is common during pregnancy because hormones cause the digestive system to slow down.
• A weak lower esophageal sphincter. If this valve is weak, it will not close properly, and reflux will occur frequently. This is a rare cause of mild GERD, but among people who have severe GERD, about 25% have this problem.¹
• Hiatal hernia. GERD is common among people with a hiatal hernia. GERD symptoms in these people can vary from mild to severe.
• Slow digestion. If food stays in your stomach too long before it goes to the small intestine (called delayed gastric emptying), the stomach contents are more likely to get pushed up into the esophagus and cause heartburn.
• Overfull stomach. Having a very full stomach-such as from eating a very large meal-increases the likelihood that the lower esophageal sphincter will relax and allow stomach juices to back up (reflux) into your esophagus.

If the stomach juice that backs up into the esophagus is not removed quickly, it can irritate the esophagus and cause the burning, warmth, heat, or pain just behind the breastbone. This feeling is commonly referred to as heartburn. Normally the acid is quickly pushed back into the stomach by squeezing movements that move down the esophagus (peristalsis). Swallowing saliva, which has a natural antacid (bicarbonate) that helps protect the lining of the esophagus, helps neutralize the acid.