With gravity's help, a muscular valve called the lower esophageal sphincter, or LES, keeps stomach acid in the stomach. The LES is located where the esophagus meets the stomach -- below the rib cage and slightly left of center. Normally it opens to allow food into the stomach or to permit belching; then it closes again. But if the LES opens too often or does not close tight enough, stomach acid can reflux, or seep, into the esophagus and cause the burning sensation.
Occasional heartburn isn't dangerous, but chronic heartburn or gastroesophageal reflux disease (GERD) can sometimes lead to serious problems.
Heartburn is a weekly occurrence for about 20% of Americans and very common in pregnant women.
What Causes Heartburn?
The basic cause of heartburn is a lower esophageal sphincter, or LES, that doesn't tighten as it should. Two excesses often contribute to this problem: too much food in the stomach (overeating) or too much pressure on the stomach (frequently from obesity, pregnancy, or constipation). Certain foods commonly relax the LES, including tomatoes, citrus fruits, garlic, onions, chocolate, coffee, alcohol, caffeinated products, and peppermint. Meals high in fats and oils (animal or vegetable) often lead to heartburn, as do certain medications. Stress and lack of sleep can increase acid production and can cause heartburn. And smoking, which relaxes the LES and stimulates stomach acid, is a major contributor.