GERD is caused by a malfunction of the muscular valve at the bottom of your esophagus, called the lower esophageal sphincter (LES). This valve normally opens to let food into your stomach and closes to keep stomach acid from flowing back up. When it doesn’t work properly, acid repeatedly washes into the esophagus, causing the burning and irritation that defines gastroesophageal reflux disease. Over 825 million people worldwide had GERD as of 2021, and the number continues to rise.
How the Anti-Reflux Valve Fails
The LES sits where your esophagus meets your stomach, acting as a one-way gate. In a healthy system, it stays closed except during swallowing. Two specific patterns of dysfunction drive most cases of GERD.
The first and most common is an abnormally high rate of spontaneous relaxations. Your LES relaxes briefly on its own throughout the day, even in healthy people. This is normal and allows you to burp. But people with GERD experience these relaxations far more frequently than people without it, and each one creates an opening for acid to escape upward into the esophagus.
The second pattern is chronically weak resting pressure in the valve itself. When the LES doesn’t maintain enough baseline tone, it can’t hold back the contents of your stomach, especially when pressure builds from a large meal, bending over, or lying down. Current evidence points to faulty nerve signaling as the primary reason the valve loses its strength, though the muscle tissue itself can also deteriorate over time.
The Role of Hiatal Hernia
A hiatal hernia occurs when the upper portion of your stomach pushes up through the diaphragm, the large muscle separating your chest from your abdomen. This is significant because the diaphragm normally wraps around the LES and reinforces it, essentially giving the valve extra support.
When a hiatal hernia pulls the LES up into the chest cavity, two things happen. First, the valve moves out of the zone of positive pressure in your abdomen and into the low-pressure environment of your chest, making it less effective at staying closed. Second, people with hiatal hernias tend to have longer episodes of spontaneous valve relaxation, particularly at night, which means more prolonged acid exposure while you sleep. This is one reason nighttime reflux can be especially damaging.
When Your Esophagus Can’t Protect Itself
Acid reflux alone doesn’t always cause injury. Your body has two built-in defenses: mechanical clearance and chemical clearance. Mechanical clearance relies on the rhythmic contractions of your esophagus (peristalsis) to push refluxed acid back down into the stomach. Chemical clearance comes from your saliva, which contains bicarbonate that neutralizes small amounts of acid on contact.
When either system is impaired, the esophagus stays exposed to acid for longer periods. Abnormal peristalsis, which can result from nerve or muscle disorders in the esophagus, leads to slow and inefficient clearing. Conditions that reduce saliva production, such as certain autoimmune diseases or simply sleeping (when saliva flow drops dramatically), also leave the esophagus more vulnerable. This is why GERD symptoms often feel worse at night: you’re lying flat, you produce less saliva, and gravity can no longer help move acid downward.
Delayed Stomach Emptying
In about one-third of GERD patients, the stomach takes longer than normal to empty its contents into the small intestine. When food and acid sit in the stomach for extended periods, pressure builds, and there’s simply more material available to reflux upward whenever the valve relaxes.
Interestingly, the symptoms of delayed stomach emptying overlap so heavily with typical GERD symptoms that you can’t distinguish between them based on how you feel. Regurgitation was present in roughly 80% of patients regardless of whether their stomachs emptied normally or slowly. This means delayed emptying can quietly worsen GERD without producing any unique warning signs.
Lifestyle and Dietary Factors
Several everyday habits increase reflux by either relaxing the LES, increasing stomach pressure, or both. Excess body weight is one of the strongest modifiable risk factors. Fat around the abdomen presses against the stomach and forces acid upward, while also appearing to weaken valve function over time.
Certain foods relax the LES directly. Chocolate, peppermint, caffeine, alcohol, and high-fat meals all reduce the valve’s resting tone, making reflux more likely in the hours after eating. Acidic foods like tomatoes and citrus don’t necessarily cause more reflux events, but they irritate an already inflamed esophagus and make symptoms feel worse. Eating large meals or eating within two to three hours of lying down gives acid more opportunity to escape while the valve is naturally more relaxed during digestion.
Smoking weakens the LES and reduces saliva production at the same time, effectively undermining both the barrier and the cleanup system. Even moderate smoking has a measurable impact on valve pressure.
Medications That Weaken the Valve
A number of commonly prescribed medications reduce LES pressure as a side effect. Calcium channel blockers used for blood pressure, sedatives in the benzodiazepine family, asthma medications containing aminophylline, and nitrate-based heart medications all relax the smooth muscle of the valve. Anticholinergic drugs, found in many allergy medications and bladder control treatments, do the same.
If you started experiencing reflux symptoms around the same time you began a new medication, the drug may be contributing. Some of these medications also irritate the esophageal lining directly, compounding the problem.
Pregnancy and Hormonal Changes
GERD affects a large proportion of pregnant women, particularly in the second and third trimesters. Rising levels of progesterone relax smooth muscle throughout the body, including the LES. At the same time, the growing uterus increases abdominal pressure, pushing stomach contents upward. This combination makes pregnancy one of the most common temporary causes of reflux. Symptoms typically resolve after delivery once hormone levels normalize and abdominal pressure decreases.
Long-Term Risks of Chronic Reflux
When acid repeatedly damages the esophageal lining over years, the tissue can undergo a transformation called Barrett’s esophagus, where the normal cells are replaced by a type more resistant to acid but also more prone to becoming cancerous. For people with Barrett’s who show no precancerous changes on biopsy, the annual risk of developing esophageal cancer is low, roughly 0.1% to 0.4% per year. That risk climbs to about 1% per year if early precancerous changes are present, and above 5% per year with more advanced changes.
These numbers are small in any given year, but they accumulate over decades of uncontrolled reflux. This is the main reason persistent GERD warrants treatment rather than simply tolerating the discomfort. Controlling acid exposure protects the esophageal lining and substantially reduces the chance of these cellular changes taking hold.