According to the British medical journal The Lancet, heartburn is pretty common. In fact, 25 percent of Americans report experiencing heartburn at least once a month, 12 percent at least once per week and 5 percent daily. So what is heartburn? And what about gastroesophageal reflux disease (GERD)? Well, here's a guide to provide a bit more understanding of that burning sensation in your chest.

Q. Why is it called heartburn?

A. "Heartburn is often sensed as a burning feeling behind the middle of the lower to middle of the chest, giving the sense that it may be coming from the heart," says Dr. Philip Jaffe, an associate professor of medicine at Yale University School of Medicine.

Q. What is happening, biologically speaking?

A. According to Dr. David A. Peura, a professor of medicine at the University of Virginia Health System, "Acid that's normally produced by the stomach is washing back up into the esophagus and irritating its lining. This is generally because the muscle between the stomach and esophagus is weak or not working properly."

Q. What does heartburn feel like?

A. "The typical sensation is a burning in the lower chest that moves toward the neck and is often associated with a bitter taste in the back of the mouth. It typically occurs after eating a large meal, bending over at the waist, or lying down soon after eating," says Jaffe.

Q. What causes heartburn?

A. According to Jaffe, there are a variety of causes, but anything that either weakens or overwhelms the lower esophageal sphincter (the ring of muscle or "valve" at the lower end of the esophagus), decreases stomach emptying (a condition called "gastroparesis" or mechanical gastric outlet obstruction) and/or reduces the ability of the esophagus to push food down to the stomach can cause heartburn. Common causes are obesity, excessive alcohol use, fatty food intake, eating late at night, smoking, medications, hernias, pregnancy, diabetes mellitus and scleroderma.

Q. What is GERD?

A. This is the condition that causes heartburn. It occurs when the lower esophageal sphincter does not close properly and stomach contents leak back into the esophagus.

Q. Do spicy foods cause heartburn and/or GERD?

A. Spicy foods can further irritate an esophagus that has been damaged by acid reflux, and irritation of the lining of the esophagus is what causes the symptoms of heartburn, says Dr. Stuart Spechler, a professor of medicine at University of Texas Southwestern Medical Center at Dallas.

Q. Are there foods that help relieve heartburn?

A. No specific foods treat heartburn. Swallowing most liquids will clear esophageal acid and give temporary relief. Chewing gum or sucking on hard candy may stimulate saliva, which contains bicarbonate — our natural antacid," recommends Peura.

Q. Can heartburn be dangerous?

A. "Severe heartburn that does not improve with over-the-counter medication and/or is associated with 'warning signs or symptoms,' including weight loss, difficulty or painful swallowing, vomiting blood, associated hoarseness or persistent cough or sore throat, abrupt onset at an older age, usually over 50, should be evaluated by a healthcare provider," says Peura.

Q. What are the long-term complications of GERD or heartburn?

A. Inflammation of the esophagus from stomach acid can cause bleeding or ulcers. And, scars from tissue damage ("strictures") can narrow the esophagus and make swallowing difficult. Some people develop Barrett's esophagus, where the normal lining is replaced by one that can sometimes transform into cancer over time, says Jaffe.

Q. How are GERD and heartburn treated?

A. Depending on severity, treatment may involve lifestyle changes (e.g., quit smoking, lose weight, eat low-fat foods, minimize caffeine), checking medications to see if they contribute to your symptoms, using antacids, foaming agents (e.g., Gaviscon) or H2 blockers (e.g., Zantac), proton pump inhibitors and even surgery.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.