GERD happens when stomach acid repeatedly flows back into your esophagus, and the causes range from a malfunctioning valve at the top of your stomach to excess body weight, certain medications, and even your genes. Most cases involve more than one contributing factor working together, which is why GERD can be tricky to pin down and why it affects people so differently.
How the Anti-Reflux Barrier Fails
At the junction where your esophagus meets your stomach sits a short band of muscle called the lower esophageal sphincter (LES). This muscle is only about 2 to 3 centimeters long, but it acts as a one-way valve, staying closed to keep stomach acid where it belongs and opening briefly when you swallow food. In healthy people, its resting pressure sits between 10 and 30 mm Hg. Working alongside it, a ring of muscle in your diaphragm wraps around the same junction and squeezes tighter when you cough, strain, or take a deep breath, providing a second layer of protection.
When GERD develops, the problem usually isn’t that this valve is permanently weak. Instead, most reflux episodes happen during what are called transient relaxations: moments when the sphincter opens inappropriately, often triggered by the stomach stretching after a meal. Everyone experiences these relaxations, but people with GERD have them more frequently, and more acid escapes each time. A smaller group of GERD patients do have chronically low sphincter pressure, but this is relatively uncommon and mostly seen in people with connective tissue conditions like scleroderma.
Hiatal Hernia
A hiatal hernia occurs when part of your stomach pushes up through the opening in your diaphragm and into your chest cavity. This displaces the lower esophageal sphincter away from the diaphragm muscle that normally reinforces it, effectively splitting your anti-reflux barrier into two separate, weaker components. The herniated portion of the stomach also gets trapped between these two structures, creating a pocket of pressure that makes reflux more likely.
Between 50% and 94% of people with GERD have a sliding hiatal hernia, making it one of the most common anatomical findings in reflux patients. Not everyone with a hiatal hernia develops symptoms, but larger hernias are more strongly linked to acid exposure and esophageal damage.
Excess Body Weight
Carrying extra weight around your midsection increases pressure inside your abdomen, which pushes against the stomach and makes it harder for the sphincter to stay closed. A meta-analysis published in the Annals of Internal Medicine found a clear dose-response relationship: people with a BMI between 25 and 30 (overweight) had about a 43% higher risk of GERD symptoms compared to those at a normal weight. For people with a BMI over 30 (obese), the risk nearly doubled.
The consequences go beyond heartburn. The same analysis found that the risk of esophageal adenocarcinoma, a serious complication of long-standing reflux, was 52% higher in overweight individuals and 178% higher in obese individuals. Even modest weight gain can shift someone from occasional reflux into chronic GERD, and weight loss is one of the few lifestyle changes consistently shown to improve symptoms.
Delayed Stomach Emptying
Your stomach is designed to grind food and release it into the small intestine at a steady pace. When that process slows down, a condition called gastroparesis, food and acid sit in the stomach much longer than normal. This prolonged retention does three things that promote reflux: it increases the volume of material available to wash back up, it raises pressure inside the stomach, and it stimulates more acid production.
Perhaps most importantly, a stomach that stays full and distended triggers more of those transient sphincter relaxations described earlier. So gastroparesis doesn’t just give reflux more material to work with. It actively opens the door for it. People with diabetes are especially prone to gastroparesis, which is one reason GERD rates are higher in that group.
Pregnancy
GERD is extremely common during pregnancy, particularly in the second and third trimesters. Rising progesterone levels relax smooth muscle throughout the body, including the lower esophageal sphincter, reducing its ability to stay closed. Progesterone also slows gastric emptying, meaning food lingers in the stomach longer.
On top of the hormonal effects, the growing uterus physically displaces the stomach upward and increases abdominal pressure. This combination of a weaker sphincter, slower digestion, and mechanical compression makes reflux almost inevitable for many pregnant women. Symptoms typically resolve after delivery once hormone levels return to normal and the uterus shrinks.
Medications That Worsen Reflux
Several common drug classes can relax the lower esophageal sphincter or irritate the esophageal lining directly. Among the most notable are calcium channel blockers, nitrates, and ACE inhibitors, all widely prescribed for high blood pressure and heart disease. Statins (cholesterol-lowering drugs) can also contribute. These medications lower sphincter pressure as a side effect, making it easier for acid to escape the stomach.
Pain relievers like ibuprofen and aspirin irritate the esophageal and stomach lining and can amplify the damage from reflux that’s already occurring. If you’re taking any of these medications and noticing worsening heartburn, it’s worth discussing alternatives or timing adjustments with your prescriber rather than stopping them on your own.
Eating Habits and Meal Timing
When you eat matters almost as much as what you eat. Lying down with a full stomach lets gravity work against you, and the data on this is striking. One study found that people who went to bed less than three hours after dinner were 7.45 times more likely to experience reflux compared to those who waited four hours or more. The standard recommendation is to finish eating at least three hours before lying down.
Large meals are a direct trigger because they stretch the stomach, prompting those transient sphincter relaxations. High-fat foods slow gastric emptying, keeping the stomach full longer. Alcohol, coffee, chocolate, and carbonated drinks are also well-known triggers, though individual sensitivity varies widely. Some people can drink coffee without issues while a single glass of wine sets off hours of burning. Tracking your own patterns matters more than following a generic list of foods to avoid.
Genetic Factors
GERD runs in families, and it’s not just because families share eating habits. Twin studies estimate that about 31% of the risk for developing GERD is inherited. Researchers have identified several genetic variations linked to higher susceptibility, including changes in genes involved in the development of the muscles and connective tissue around the esophageal junction, immune signaling, and DNA repair.
This genetic contribution helps explain why some people develop severe GERD despite being at a healthy weight and following all the right lifestyle habits, while others with multiple risk factors never experience significant symptoms. Genetics likely influence sphincter muscle tone, the sensitivity of the esophageal lining to acid, and how efficiently the esophagus clears refluxed material.
How Multiple Causes Overlap
GERD rarely stems from a single cause. A person with a mild hiatal hernia might manage fine until they gain 20 pounds, which increases abdominal pressure enough to overwhelm their already compromised barrier. Someone with a genetic predisposition toward lower sphincter tone might not develop symptoms until pregnancy or a new blood pressure medication tips the balance. The condition is best understood as a threshold problem: your anti-reflux defenses can absorb a certain amount of strain, but once enough factors stack up, acid starts getting through regularly.
This is also why treatment works on multiple fronts. Acid-suppressing medications reduce the damage from reflux episodes, but addressing the underlying causes, whether that’s weight loss, meal timing, medication review, or hernia repair, targets why the reflux is happening in the first place.