Acid reflux happens when stomach acid flows backward into the esophagus, the tube connecting your mouth to your stomach. Over 825 million people worldwide deal with it. The causes range from a weak muscular valve at the top of your stomach to everyday habits like what you eat, how much you weigh, and which medications you take.
How the Anti-Reflux Barrier Fails
At the bottom of your esophagus sits a ring of muscle called the lower esophageal sphincter (LES). In healthy people, this valve maintains a resting pressure between 10 and 30 mmHg, keeping stomach contents where they belong. It opens briefly when you swallow, then snaps shut. When this valve weakens, loosens, or relaxes at the wrong times, acid escapes upward.
The LES doesn’t work alone. It’s part of a broader barrier that includes the diaphragm muscle and a ligament that anchors the junction between the esophagus and stomach. All three structures have to coordinate. In people with chronic reflux, the diaphragm’s contribution to that seal is measurably weaker at rest compared to healthy people, and the junction itself becomes two to three times more stretchable than normal. That excess flexibility lets more acid through and triggers more frequent valve relaxations.
One of the most common mechanical triggers is something called a transient lower esophageal sphincter relaxation. Unlike the brief opening that happens when you swallow (lasting about 6 to 8 seconds), these spontaneous relaxations last more than 10 seconds and aren’t triggered by swallowing at all. They’re designed to let gas escape from the stomach, but when they happen too often, liquid stomach contents come along for the ride.
Hiatal Hernia
A hiatal hernia occurs when the upper part of your stomach pushes through the small opening in the diaphragm (called the hiatus) and bulges into the chest cavity. This physically separates the two components of the anti-reflux barrier: the LES and the diaphragm. Normally they sit right on top of each other, reinforcing the seal. When they’re pulled apart, even by a centimeter or two, the barrier becomes much less effective.
Small hiatal hernias are common and often cause no symptoms at all. Larger ones allow food and acid to back up into the esophagus more easily because the stomach’s position above the diaphragm eliminates gravity’s help in keeping contents down. Hiatal hernias are one of the most frequent findings in people with persistent, hard-to-treat reflux.
Foods That Trigger Reflux
Certain foods relax the LES and slow digestion, keeping food in the stomach longer and giving acid more opportunity to escape. The most reliable triggers are foods high in fat, salt, or spice:
- High-fat foods: fried food, fast food, pizza, bacon, sausage, cheese, and processed snacks like potato chips
- Spicy seasonings: chili powder, cayenne, black pepper, and white pepper
- Acidic foods: tomato-based sauces and citrus fruits, which have a low pH and directly irritate the esophageal lining
- Chocolate and peppermint: both relax the LES
- Carbonated beverages: the gas increases stomach pressure and can force the valve open
You don’t necessarily need to avoid every item on this list permanently. Reflux triggers are individual. Some people can handle tomato sauce but not fried food, or vice versa. Paying attention to which foods consistently cause symptoms is more useful than following a blanket elimination diet.
Excess Weight and Abdominal Pressure
Carrying extra weight, especially around the midsection, increases pressure on the stomach and pushes its contents upward toward the esophagus. The relationship between body weight and reflux is well established and dose-dependent: the heavier you are, the higher your risk.
A large cohort study found that people with obesity had roughly 29% higher risk of developing chronic reflux compared to people at a normal weight. Those who were overweight but not yet obese still had about 19% higher risk. Even the jump from overweight to obese carried a meaningful increase. This makes weight management one of the most impactful lifestyle changes for reducing reflux symptoms, particularly when excess weight is concentrated in the abdomen.
Pregnancy
Up to two-thirds of pregnant women experience heartburn, and two separate mechanisms explain why. The hormone progesterone, which rises dramatically during pregnancy, relaxes smooth muscle throughout the body. That includes the LES. Progesterone also slows the entire digestive process, so food sits in the stomach longer, creating more opportunity for acid to back up.
As pregnancy progresses, the growing uterus adds a second layer of pressure. It pushes upward against the stomach, physically compressing it and forcing contents toward the esophagus. This is why reflux tends to worsen in the third trimester and typically resolves after delivery.
Smoking
Nicotine weakens the esophageal sphincter directly. Smoking also reduces saliva production, which matters because saliva is slightly alkaline and helps neutralize small amounts of acid that reach the esophagus. People who smoke and already have occasional reflux often find their symptoms become significantly more frequent and severe. Quitting smoking improves LES function over time.
Medications That Worsen Reflux
Several common medications can either irritate the esophagus directly or weaken the LES, making reflux worse. They fall into two categories.
Some medications damage the esophageal lining on the way down, creating a burning pain that mimics reflux. These include common pain relievers like ibuprofen and aspirin, certain antibiotics, iron supplements, and osteoporosis medications taken by mouth. Taking these with a full glass of water and staying upright afterward can reduce the irritation.
Other medications actually increase acid reflux by relaxing the LES or slowing stomach emptying. Calcium channel blockers and nitrates (used for blood pressure and heart disease), opioid painkillers, tricyclic antidepressants, and medications for overactive bladder all fall into this group. If you take one of these and notice new or worsening heartburn, it’s worth discussing alternatives with whoever prescribed it.
Delayed Stomach Emptying
When the stomach empties slower than normal, a condition called gastroparesis, food and acid accumulate and the stomach becomes distended. That distension makes it physically easier for acid to escape through the top of the stomach into the esophagus. Gastroparesis can result from diabetes, certain surgeries, or nerve damage, and reflux is one of its most common secondary symptoms. People with gastroparesis often find that standard acid-reducing medications help the burning but don’t fully resolve the problem, because the underlying issue is mechanical pressure from a stomach that isn’t emptying properly.
Eating Habits and Timing
Beyond what you eat, when and how you eat plays a significant role. Large meals stretch the stomach and increase pressure on the LES. Eating within two to three hours of lying down removes gravity from the equation, making it easier for acid to travel up the esophagus. This is why late-night eating is one of the most consistent triggers people report.
Eating quickly tends to cause you to swallow more air, which increases stomach pressure. Tight clothing around the waist, bending over after meals, and vigorous exercise right after eating can all produce the same upward pressure effect. For many people, adjusting these patterns produces noticeable improvement even without medication or dietary changes.