Acid reflux happens when stomach acid flows backward into your esophagus, the tube connecting your mouth to your stomach. A ring of muscle at the bottom of that tube is supposed to close after food passes through, but when it relaxes at the wrong time or doesn’t seal tightly enough, acid escapes upward. Roughly 10% of the global population deals with this regularly, and the causes range from what you eat to how your body is built.
The Muscle That’s Supposed to Keep Acid Down
At the base of your esophagus sits a valve made of smooth muscle. When it’s working properly, it opens to let food into your stomach and then snaps shut. Acid reflux occurs when this valve weakens, loosens, or opens when it shouldn’t. Nearly every cause of reflux traces back to something affecting this valve’s ability to stay closed, or something increasing pressure in your stomach that forces acid past it.
Foods That Trigger Reflux
Certain foods relax that valve and slow digestion, letting food sit in your stomach longer than it should. The combination creates ideal conditions for acid to push upward. The most common offenders are foods high in fat, salt, or spice: fried food, fast food, pizza, fatty meats like bacon and sausage, cheese, and processed snacks like potato chips.
Other foods cause problems through different mechanisms. Tomato-based sauces and citrus fruits are highly acidic on their own. Chocolate and peppermint directly relax the esophageal valve. Carbonated beverages introduce gas that increases stomach pressure. Coffee is a frequent trigger for many people, partly because caffeine loosens that same valve. You don’t necessarily need to eliminate all of these, but identifying which ones affect you personally is one of the most effective ways to reduce episodes.
Body Weight and Stomach Pressure
Carrying extra weight, especially around your midsection, physically compresses your stomach. This raises the pressure inside your abdomen and pushes stomach contents upward toward the esophageal valve. Excess abdominal fat also increases the physical distance between the two structures that work together to prevent reflux: the muscular valve and a section of the diaphragm that reinforces it. When those two components get separated, neither works as effectively on its own. Even modest weight loss can reduce reflux symptoms for this reason.
How Your Anatomy Can Work Against You
Your diaphragm, the large muscle separating your chest from your abdomen, has a small opening called the hiatus that your esophagus passes through on its way to your stomach. In a hiatal hernia, part of your stomach pushes up through that opening into your chest. This repositioning disrupts the natural angle between the esophagus and stomach, making it far easier for acid to flow the wrong direction. Small hiatal hernias often cause no symptoms at all, but a large one can allow significant amounts of food and acid to back up into the esophagus.
Slow Stomach Emptying
Your stomach is designed to break down food and move it into the small intestine within a few hours. When that process slows down, food and acid linger longer than they should, increasing the chances of reflux. About 25% of people diagnosed with chronic reflux have measurably delayed stomach emptying at the four-hour mark after a solid meal. This slowdown can result from nerve damage (common in diabetes), certain medications, or sometimes no identifiable cause. The tricky part is that symptoms of slow emptying overlap heavily with regular reflux, so it often goes unrecognized without specific testing.
Medications That Make It Worse
A surprisingly long list of common medications can contribute to acid reflux. Some directly irritate the esophagus on the way down, including certain antibiotics, iron supplements, and potassium supplements. Others actually relax the esophageal valve or increase acid production. Blood pressure medications like calcium channel blockers and nitrates fall into this category, along with some sedatives, opioid pain medications, certain antidepressants, and medications prescribed for overactive bladder. If your reflux started or worsened after beginning a new medication, that connection is worth exploring with whoever prescribed it.
Pregnancy and Hormonal Changes
Up to two-thirds of pregnant women experience acid reflux, and hormones are a major reason why. Progesterone, which rises steadily throughout pregnancy, has a direct relaxing effect on smooth muscle, including the esophageal valve. As progesterone climbs, the valve’s resting pressure drops, making it progressively easier for acid to escape. The growing uterus compounds the problem in later months by pushing the stomach upward and increasing abdominal pressure. This is why reflux tends to worsen as pregnancy progresses and typically resolves after delivery.
Smoking and Your Esophagus
Smoking contributes to reflux through a mechanism most people don’t expect: it reduces your saliva’s ability to neutralize acid. Clearing acid from the esophagus is a two-step process. First, the muscular contractions of swallowing push the liquid back down. Then, swallowed saliva neutralizes whatever residual acid clings to the esophageal lining. Saliva contains a natural buffering compound that does this work, and smokers produce significantly less of it. Research shows that smoking acutely prolongs the time acid stays in contact with the esophagus, and the reduction in salivary buffering is the primary reason. Peristaltic function (the squeezing motion that moves things down) is no different in smokers versus nonsmokers. It’s the neutralization step that fails.
Eating Habits and Timing
How and when you eat matters as much as what you eat. Large meals stretch the stomach and increase pressure against the valve. Eating within two to three hours of lying down removes gravity’s help in keeping acid where it belongs. Eating quickly means swallowing more air, which adds to stomach pressure. These are among the most modifiable causes of reflux, and adjusting meal size and timing often produces noticeable improvement without any other changes.
Why Reflux Gets Worse at Night
Lying flat eliminates the gravitational advantage that keeps acid in your stomach during the day. Your swallowing rate drops during sleep, so less saliva reaches the esophagus to neutralize acid. And without conscious swallowing to trigger the muscular contractions that clear the esophagus, acid that does escape tends to pool longer. Elevating your head and upper body by about six inches uses gravity to counteract this. Sleeping on your left side also helps because of the anatomical relationship between the stomach and esophagus: in this position, the junction where they meet sits above the pool of stomach acid rather than below it. The American Gastroenterological Association specifically recommends left-side sleeping for this reason.
When Occasional Reflux Becomes GERD
Everyone gets acid reflux occasionally. It crosses into gastroesophageal reflux disease, or GERD, when symptoms occur two or more times per week, or when the esophagus shows signs of damage such as erosions, narrowing, or precancerous cellular changes. The American College of Gastroenterology considers regular use of over-the-counter antacids (more than twice a week) a signal that something more persistent is going on. Left untreated over years, chronic acid exposure can lead to a condition called Barrett’s esophagus, where the esophageal lining changes in ways that increase the risk of esophageal cancer. That progression is uncommon, but it’s the reason persistent reflux is worth addressing rather than simply managing with antacids indefinitely.