GERD happens when stomach acid repeatedly flows back into your esophagus, and the valve designed to prevent that backflow isn’t doing its job. About 10% of the global population lives with the condition, and the number of cases has nearly doubled since 1990. The reasons behind it range from a weakened muscular valve to body composition, hormones, and what you eat.
The Valve That Keeps Acid Down
At the bottom of your esophagus sits a ring of muscle called the lower esophageal sphincter (LES). It works like a one-way gate: it opens to let food into your stomach, then closes to keep everything from splashing back up. In healthy people, this muscle maintains a steady resting pressure between 10 and 30 mmHg, enough to form a reliable seal.
The LES doesn’t work alone. Your diaphragm, the large dome-shaped muscle you use to breathe, wraps around the same spot where the esophagus meets the stomach. Every time you inhale, the diaphragm squeezes that junction tighter. Together, the LES and the diaphragm create a double lock against reflux.
GERD develops when one or both of these mechanisms weaken. In people with reflux esophagitis (visible damage to the esophageal lining), the LES resting pressure is significantly lower than normal, and the sphincter itself is physically shorter. A shorter, weaker valve simply can’t contain stomach contents the way a healthy one can.
How the Valve Fails
Your LES relaxes briefly throughout the day even when you aren’t swallowing. These episodes, called transient relaxations, normally let trapped gas escape from your stomach. Each one lasts more than 10 seconds, and in most people they’re harmless. But in GERD patients, the junction between the esophagus and stomach is two to three times more distensible than normal, meaning it stretches open more easily. When the valve relaxes in a stretchier junction, liquid acid comes up along with the gas.
People with GERD also tend to have weaker diaphragmatic support around that junction. When you cough, bend over, or strain, your diaphragm normally acts as a backup sphincter, clamping down to prevent a surge of acid. If the diaphragm’s grip at that point is loose, those sudden spikes in abdominal pressure push stomach contents straight through.
What a Hiatal Hernia Changes
A hiatal hernia occurs when part of the stomach slides upward through the opening in the diaphragm, so the stomach and the LES no longer sit in the same place. This separates the two components of that double lock. Instead of the diaphragm reinforcing the LES, each one works in isolation, and neither is strong enough on its own.
The wider the gap between the two, the worse the reflux tends to be. When the separation reaches 2 centimeters or more, the diaphragm can no longer generate meaningful pressure during breathing, and the LES is left to hold the line alone. Hiatal hernias are also more common in people who carry excess weight, which compounds the problem.
When the Stomach Empties Too Slowly
Your stomach is designed to process a meal and move it along into the small intestine within a few hours. When that emptying process is delayed, food and liquid accumulate, stretching the upper stomach. That distension pulls the LES open from below, shortening it in much the same way inflating a balloon shortens its neck. A shortened sphincter paired with a fuller stomach creates the perfect setup for reflux, especially after meals.
Slow gastric emptying isn’t always a separate condition. It can be triggered by high-fat meals, certain medications, or fluctuations in blood sugar. For some people, it’s the hidden driver behind reflux that doesn’t respond well to typical acid-reducing treatments.
Your Esophagus Has Its Own Defenses
Even in healthy people, small amounts of acid reach the esophagus occasionally. Normally, this isn’t a problem because the esophagus clears acid in two quick steps. First, one or two waves of muscular contraction sweep nearly all the acid back down into the stomach. Then swallowed saliva, which contains bicarbonate (a natural acid neutralizer), mops up whatever trace amount remains.
GERD can gain a foothold when either of these defenses falters. Anything that reduces saliva production, like sleeping, mouth breathing, smoking, or certain medications, slows down that second neutralizing step. And if the muscular contractions in your esophagus are weak or uncoordinated, the first step fails too, leaving acid sitting on the lining longer than it should.
Why Body Weight Matters
Excess abdominal fat doesn’t just sit passively. It physically increases the pressure inside your abdomen, pushing against the stomach and forcing the contents upward against the LES. That extra pressure also displaces the sphincter from its ideal position, weakening its seal. This is why GERD symptoms often improve with even modest weight loss.
Obesity also raises reflux risk through less obvious pathways. People who carry significant abdominal weight are more likely to develop a hiatal hernia. There’s also evidence that nerve signaling abnormalities associated with obesity can increase the output of bile and digestive enzymes, making the refluxed material more irritating to the esophageal lining. So it’s not just that reflux happens more often; the reflux itself may be more damaging.
Foods and Drinks That Relax the Valve
Certain substances directly lower the pressure in your LES, making reflux more likely in the hours after you consume them. The most well-established culprits are alcohol, chocolate, coffee, high-fat foods, and mint (especially peppermint). These don’t cause GERD on their own, but in someone whose valve is already borderline, they can be the difference between a comfortable evening and one spent with heartburn.
High-fat meals do double duty: they relax the sphincter and slow gastric emptying at the same time. That’s why a greasy late-night meal is one of the most reliable triggers. Eating closer to bedtime also matters because lying down removes gravity from the equation, leaving acid free to pool in the esophagus.
Hormones and Reflux
Estrogen and progesterone both promote the production of nitric oxide, a compound that relaxes smooth muscle throughout the body, including the LES. This is why GERD is so common during pregnancy: rising progesterone levels soften the sphincter, while the growing uterus increases abdominal pressure from below. The combination is powerful enough that up to two-thirds of pregnant women experience reflux symptoms.
Hormonal influence extends beyond pregnancy. Postmenopausal women on hormone replacement therapy also show higher rates of reflux, reinforcing the connection between these hormones and sphincter tone.
Medications That Contribute
Several classes of medication can worsen reflux by lowering LES pressure, slowing esophageal contractions, or directly irritating the esophageal lining. Blood pressure medications that relax blood vessels (calcium channel blockers), heart medications containing nitrates, and some sedatives are among the most commonly implicated. Anti-inflammatory painkillers can also irritate the esophagus on the way down, compounding the problem. If you notice reflux worsening after starting a new medication, that connection is worth raising with whoever prescribed it.
Why It Becomes Chronic
A single episode of acid reflux is normal. GERD becomes a disease when the factors above overlap and persist. Someone with a mildly weak sphincter might never notice symptoms until they gain weight, start a new medication, or develop a small hiatal hernia. Each additional factor stacks on top of the others, tipping the balance from occasional reflux to chronic damage.
Once the esophageal lining is inflamed, it becomes less effective at clearing acid, which leads to more inflammation, creating a cycle that can be difficult to break without addressing the underlying contributors. That’s why effective management usually involves more than just suppressing acid. It means identifying which combination of mechanical, dietary, and physiological factors is driving your particular case.