Chronic acid reflux happens when the barrier between your stomach and esophagus fails repeatedly, allowing stomach acid to wash upward into a tube that isn’t built to handle it. Globally, more than 825 million people had gastroesophageal reflux disease (GERD) as of 2021, and that number has been climbing steadily since 1990. The causes range from a malfunctioning valve at the top of your stomach to excess body weight, certain medications, and even the position you sleep in.
The Valve That’s Supposed to Keep Acid Down
At the junction where your esophagus meets your stomach sits a ring of muscle called the lower esophageal sphincter (LES). It opens to let food through, then closes to keep acid where it belongs. In people with chronic reflux, this valve either relaxes when it shouldn’t or stays too weak at rest to form a reliable seal.
The most common mechanism is something called a transient relaxation. The valve opens briefly even though you haven’t swallowed anything. When this happens, the sphincter relaxes, the surrounding diaphragm muscle stops contracting, and the esophagus shortens slightly, all of which create an open pathway for acid. These inappropriate relaxations are triggered by distension in the upper stomach, which is why eating a large meal so reliably brings on symptoms.
Some people also have chronically low resting pressure in the sphincter itself. Research shows that the diaphragm muscle surrounding this junction generates less pressure in GERD patients than in healthy people, even at rest. On top of that, the junction can become overly compliant, meaning it stretches open more easily under pressure. The more compliant it is, the more frequently acid escapes upward.
How a Hiatal Hernia Changes the Equation
Your diaphragm, the dome-shaped muscle that helps you breathe, has a small opening called the hiatus where the esophagus passes through on its way to the stomach. In a hiatal hernia, the upper portion of the stomach pushes up through that opening and into the chest cavity. A small hernia may cause no symptoms at all, but a larger one disrupts the normal anatomy in two important ways: it separates the sphincter from the diaphragm (which normally reinforces it), and it creates a pocket above the diaphragm where acid can pool and easily wash back into the esophagus.
Hiatal hernias are extremely common, particularly in people over 50. They don’t guarantee chronic reflux, but they significantly raise the odds by weakening the body’s primary physical barrier against it.
The Role of Excess Body Weight
Carrying extra weight, especially around the abdomen, is one of the strongest risk factors for chronic acid reflux. The mechanism is straightforward: abdominal fat increases the pressure inside your abdomen, which in turn pushes against your stomach. That elevated pressure forces the contents of your stomach upward against the sphincter.
But it’s not just about pressure. Excess abdominal weight also physically separates the two components of the anti-reflux barrier: the sphincter itself and the surrounding diaphragm muscle. When these two structures drift apart, neither works as effectively on its own. Research published in the New England Journal of Medicine notes that waist circumference or abdominal diameter may be a better predictor of reflux risk than BMI alone, because it’s the fat around the midsection, not overall body weight, that drives the mechanical problem.
Delayed Stomach Emptying
Your stomach is designed to break food down and move it into the small intestine within a few hours. When that process slows down, a condition called gastroparesis, food sits in the stomach far longer than it should. The longer it sits, the more your stomach stretches. That stretching increases pressure and makes it easier for acid to escape out the top of the stomach into the esophagus.
Gastroparesis can result from diabetes, certain surgeries, or neurological conditions. If you feel uncomfortably full almost immediately after eating, stay bloated for hours, or frequently feel nauseous after meals alongside your reflux symptoms, delayed emptying could be a contributing factor.
Foods and Chemicals That Relax the Sphincter
Certain foods don’t just irritate the esophagus on the way down. They actively weaken the sphincter muscle. Chocolate contains a compound called methylxanthine (chemically similar to caffeine) that directly relaxes the lower esophageal sphincter, making reflux more likely after you eat it. Caffeine itself has a similar, though milder, effect. Peppermint also relaxes smooth muscle throughout the digestive tract, including the sphincter.
Fatty foods slow gastric emptying, keeping your stomach fuller and more distended for longer. Acidic foods like tomatoes and citrus don’t necessarily cause reflux on their own, but they make the acid that does reflux more irritating to the esophageal lining. Alcohol and carbonated beverages increase stomach distension and can trigger those inappropriate sphincter relaxations. The pattern matters more than any single meal: occasional chocolate won’t cause chronic reflux, but daily exposure to multiple triggers can keep the cycle going.
Medications That Weaken the Barrier
Several common prescription drugs lower the pressure in the esophageal sphincter as a side effect. Calcium channel blockers, widely prescribed for high blood pressure, relax smooth muscle throughout the body, including the sphincter. Nitrates, used for chest pain, do the same. Theophylline, a medication for asthma and other lung conditions, also reduces sphincter pressure.
If your reflux started or worsened around the time you began a new medication, it’s worth looking into whether the drug is a known contributor. Stopping or switching medications is a conversation for your prescriber, but identifying the connection is the first step.
Hormones and Pregnancy
Pregnancy is one of the most predictable triggers for acid reflux, and the cause is primarily hormonal. Rising progesterone levels relax the esophageal sphincter, reducing its ability to stay closed. Progesterone also slows the entire digestive process, which means food lingers in the stomach longer and creates more opportunity for reflux. As the pregnancy progresses, the growing uterus adds direct physical pressure on the stomach from below, compounding the problem.
This combination of hormonal relaxation and mechanical pressure is why reflux tends to worsen through each trimester. The good news is that pregnancy-related reflux typically resolves after delivery once hormone levels return to normal and the physical pressure is gone.
Sleep Position and Nighttime Reflux
Lying flat removes gravity from the equation. When you’re upright, gravity helps keep stomach contents where they belong. The moment you lie down, acid can flow sideways toward the sphincter with much less resistance, which is why many people experience their worst symptoms at night or early in the morning.
The American Gastroenterological Association recommends sleeping on your left side. This position works because of simple anatomy: the stomach curves to the left, so when you lie on that side, the junction with the esophagus sits above the pool of acid rather than submerged in it. Elevating the head of your bed by 6 to 8 inches (using a wedge or bed risers, not just extra pillows) also helps by creating a gentle downward slope that keeps acid in the stomach.
When Multiple Causes Stack Up
Chronic acid reflux is rarely caused by one thing alone. A person with a mildly weak sphincter might never have significant symptoms until they gain weight, start a calcium channel blocker, and begin eating larger evening meals. Each factor on its own might be manageable, but together they overwhelm the body’s defenses. This is also why treatment often works best when it addresses several contributors at once: losing abdominal weight, adjusting sleep position, identifying trigger foods, and reviewing medications can collectively reduce reflux far more than any single change.
The sphincter’s resting pressure also tends to decline with age, which is why reflux often develops or worsens in middle age even without an obvious new trigger. Years of mild mechanical stress, gradual weight gain, and natural muscle weakening converge to tip the balance.