Acid reflux happens when stomach acid flows backward into the esophagus, the tube connecting your mouth to your stomach. The root cause is almost always a problem with the valve at the bottom of that tube, but a surprising number of factors can make that valve malfunction, from the foods you eat to medications you take to how your body is built. Globally, over 825 million people deal with chronic acid reflux, including roughly 45 million in the United States alone.
The Valve That’s Supposed to Keep Acid Down
At the base of your esophagus sits a ring of muscle called the lower esophageal sphincter (LES). It opens to let food into your stomach, then closes to keep acid from traveling upward. When this valve doesn’t work properly, acid escapes. That’s reflux.
Two specific patterns of valve failure drive most cases. The first is when the valve relaxes at the wrong time, opening spontaneously when you haven’t swallowed anything. The second is when the valve’s resting pressure is simply too weak to stay shut against the pressure in your stomach. Both patterns trace back primarily to faulty nerve signaling rather than a structural defect in the muscle itself, though muscle weakness can play a role too.
Your diaphragm, the thin sheet of muscle separating your chest from your abdomen, acts as a backup system. It wraps around the base of the esophagus and squeezes during straining or coughing, reinforcing the valve. When this backup system is compromised, reflux becomes much more likely.
Hiatal Hernia: When Anatomy Works Against You
A hiatal hernia occurs when the upper portion of your stomach pushes up through the opening in the diaphragm where the esophagus passes through. This displaces the valve above the diaphragm, removing that critical backup squeeze. With the diaphragm no longer reinforcing the valve, acid moves into the esophagus far more easily. Not everyone with a hiatal hernia has severe reflux, but the hernia makes the anti-reflux barrier significantly less effective, especially during physical strain or after meals.
Foods That Relax the Valve
Certain foods don’t just irritate your stomach. They actively relax the valve and slow digestion, letting food sit in the stomach longer and giving acid more opportunity to escape. The most common culprits include:
- High-fat foods: fried food, fast food, fatty meats like bacon and sausage, cheese, and pizza
- Spicy foods: chili powder, black pepper, cayenne
- Acidic foods: tomato-based sauces and citrus fruits
- Chocolate and peppermint
- Carbonated beverages
These foods trigger reflux through a double mechanism. They cause the valve to loosen while simultaneously slowing the rate at which your stomach empties. The result is more acid sitting around with a weaker barrier holding it in place.
Body Weight and Physical Pressure
Excess abdominal fat increases the pressure inside your abdomen, pushing upward against the stomach and forcing acid toward the weakest point: the valve at the top. This isn’t just a general association. The rate of spontaneous valve relaxation episodes increases with both BMI and waist circumference specifically. People carrying more weight around the midsection also have higher rates of hiatal hernia, compounding the problem.
Pregnancy creates a similar dynamic. The growing uterus pushes the stomach upward, increasing pressure on the valve. Hormonal changes during pregnancy also relax smooth muscle throughout the body, including the esophageal valve. This is why reflux tends to worsen as pregnancy progresses and typically resolves after delivery.
Medications That Make Reflux Worse
A long list of common medications can trigger or worsen acid reflux through two distinct pathways. Some directly irritate the lining of the esophagus as they pass through. These include certain antibiotics, common pain relievers like ibuprofen and aspirin, iron supplements, and some osteoporosis medications.
Others weaken the valve itself or slow stomach emptying. Blood pressure medications (particularly calcium channel blockers and nitrates), opioid painkillers, sedatives, certain antidepressants, and medications for overactive bladder all fall into this category. If you started experiencing reflux around the same time you began a new medication, that connection is worth exploring with whoever prescribed it.
Slow Stomach Emptying
When your stomach takes too long to process food, a condition called gastroparesis, it becomes distended and stretched. That distension creates outward pressure in all directions, making it easier for acid to escape through the valve at the top. You might notice feeling full almost immediately after eating, persistent bloating, nausea, or a stretched sensation in the upper abdomen. Gastroparesis is most common in people with diabetes but can also result from surgery, certain medications, or nerve damage. The reflux it causes tends to be stubborn because the underlying slow motility keeps the stomach full and pressurized for hours after meals.
Why Reflux Gets Worse at Night
Three things change when you lie down, and all of them favor reflux. First, gravity stops helping. When you’re upright, gravity pulls stomach contents downward, away from the valve. Lying flat removes that advantage entirely. Second, you produce less saliva during deeper stages of sleep. Saliva is mildly alkaline and helps neutralize any acid that reaches the esophagus. Third, you swallow far less often while asleep. Swallowing is one of the main forces that pushes escaped acid back down into the stomach.
The combination means acid not only reaches the esophagus more easily at night but stays there longer, causing more damage per episode. This is why people with reflux often wake with a sore throat, hoarse voice, or bitter taste that wasn’t present at bedtime. Eating within two to three hours of lying down magnifies all of these effects because the stomach is still actively producing acid to digest your last meal.
Other Contributing Factors
Smoking weakens the esophageal valve and reduces saliva production simultaneously. Alcohol relaxes the valve and can irritate the esophageal lining directly. Family history plays a role too, suggesting a genetic component to how the valve develops and functions. Even stress, while not a direct cause of acid production, changes how you perceive pain in the esophagus. People under chronic stress report more severe symptoms at the same levels of acid exposure.
In most people, reflux results from several of these factors layering on top of each other rather than a single dramatic cause. A slightly weak valve might cause no symptoms on its own, but add 20 extra pounds, a nightly glass of wine, and a blood pressure medication, and you have a recipe for regular heartburn. Understanding which factors apply to you is the first step toward figuring out which ones you can change.