Why Do We Get Heartburn?
The burn sits right behind the breastbone, sometimes rising toward the throat with a sour taste. Despite the name, heartburn has nothing to do with the heart. It is the feeling of stomach acid going the wrong way, up into the food pipe, and it is remarkably common: a major meta-analysis pooling studies of more than 460,000 people found that about 13 percent of adults worldwide feel heartburn or regurgitation at least once a week.
Two neighbors with very different armor
Your stomach is built for acid. Its lining produces a protective layer of mucus and constantly renews itself, so it can hold a fluid roughly as acidic as battery acid without digesting itself. The esophagus, the tube that carries food down to the stomach, has no such protection. Its lining is meant for food sliding past, nothing more. When stomach contents splash up into it, the acid irritates the tissue directly, and that irritation is the burn you feel.
The valve that takes unscheduled breaks
Between the esophagus and the stomach sits a ring of muscle called the lower esophageal sphincter. It stays clamped shut most of the time and opens to let food down. For decades doctors assumed heartburn meant this valve was simply too weak. Then a classic 1982 study in the New England Journal of Medicine measured the pressure in patients and found something different: in most reflux episodes the valve's resting pressure was fine. Instead, it briefly and spontaneously relaxed at the wrong moments, opening the gate for a few seconds at a time. These transient relaxations turned out to be the main mechanism behind ordinary reflux.
That explains the everyday triggers. Anything that increases the number of ill-timed relaxations or pushes stomach contents upward against the valve encourages reflux: large and fatty meals, lying down soon after eating, and being bent over on a full stomach. A hiatal hernia, where part of the stomach slips up through the diaphragm, makes episodes more likely by disrupting the valve's anatomy. The same meta-analysis found reflux symptoms are measurably more common in people over 50, smokers, regular users of NSAID painkillers like ibuprofen, and people with obesity, each of which nudges the mechanics or the pressure balance in the wrong direction.
When the burn is a pattern
An occasional bout after a big, late meal is ordinary physiology. Gastroenterology guidelines draw the line at frequency: heartburn that shows up twice a week or more, or that comes with trouble swallowing, counts as gastroesophageal reflux disease and deserves a doctor's attention, because years of acid exposure can inflame and eventually change the esophageal lining. Antacids neutralize acid already in the esophagus for quick relief, while medicines like proton pump inhibitors reduce how much acid the stomach makes in the first place, which is why they take a day or two to reach full effect.
Facts checked: October 26, 2026
Sources: Dodds, W. J., Dent, J., Hogan, W. J., et al. (1982). Mechanisms of gastroesophageal reflux in patients with reflux esophagitis. The New England Journal of Medicine. Katz, P. O., Dunbar, K. B., Schnoll-Sussman, F. H., Greer, K. B., Yadlapati, R., and Spechler, S. J. (2022). ACG Clinical Guideline for the Diagnosis and Management of Gastroesophageal Reflux Disease. The American Journal of Gastroenterology. Eusebi, L. H., Ratnakumaran, R., Yuan, Y., et al. (2018). Global prevalence of, and risk factors for, gastro-oesophageal reflux symptoms: a meta-analysis. Gut.