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What Causes GERD (Acid Reflux)?

April 21, 2026Published date
April 21, 2026Last reviewed
Clinically reviewed by Physicians
What Causes GERD (Acid Reflux)?

Outline

GERD happens when stomach acid repeatedly flows back into the esophagus. Learn what causes it, from a weak LES and hiatal hernia to obesity, diet, and medications.

Key Takeaways

  • GERD occurs when the lower esophageal sphincter (LES) fails to stay closed properly.
  • Hiatal hernia is found in 50% to 94% of people with GERD and physically undermines the LES by displacing it above the diaphragm.
  • Obesity increases intra-abdominal pressure, raising the risk of both LES dysfunction and hiatal hernia.
  • Certain food items, medicines, and habits such as smoking, alcohol use, and fatty food consumption can also induce or worsen GERD by relaxing the lower esophageal sphincter.
  • Pregnancy, delayed emptying of the stomach, and connective tissue diseases are less common causes of GERD.

How GERD Develops: The Basic Mechanism

Located at the base of the esophagus, the lower esophageal sphincter (LES) is a muscle that allows food to move down into the stomach. Then it closes to prevent stomach acid from going up into the esophagus. When the LES fails to function correctly, the stomach acids move back up into the esophagus, causing the symptoms of GERD. Most people with GERD have a combination of structural, physiological, and lifestyle contributors rather than a single cause.

Lower Esophageal Sphincter Dysfunction

The LES fails in two distinct ways.

Low Resting Pressure

In some people, the LES does not generate enough baseline pressure to stay closed against the upward force of the stomach, allowing acid to leak continuously.

Transient LES Relaxations

The more common problem is that the LES fails to relax at the appropriate time; that is, it is stimulated by distension of the stomach after meals rather than by swallowing. These transient relaxations are the most common cause of reflux. Large meals, high-fat meals, and swallowed air are all triggers.

Hiatal Hernia

When the upper part of the stomach presses up into the diaphragm's esophageal gap, a hiatal hernia occurs. The diaphragm typically functions as a second sphincter, supporting the LES even while coughing or straining. However, the stomach pushes the LES above the support of the diaphragm in a hiatal hernia, and large hiatal hernias develop an "acid pocket" that exists even in a lying down position. Between 50% and 94% of people with GERD have a sliding hiatal hernia. These hernias become more common with age, obesity, and anything that chronically raises intra-abdominal pressure.

Obesity

Excess abdominal weight presses on the stomach from outside, pushing contents upward and increasing the gastroesophageal pressure gradient. Over time, this mechanical stress also contributes to hiatal hernia. There is also a hormonal angle. Visceral fat tissue secretes estrogen, which has a relaxing effect on smooth muscles, including the lower esophageal sphincter. The effect is dose-dependent; as BMI increases, so does the incidence and severity of symptoms, and weight reduction alleviates symptoms.

Diet and Eating Habits

While food does not structurally impair the LES, there are some foods that will provoke symptoms. Fatty foods slow down the emptying of the stomach, making it feel full and increasing the likelihood of transient LES relaxations. Chocolate, peppermint, caffeine, and alcohol relax the LES. Acidic foods such as citrus fruits and tomatoes do not impair the LES but increase the burning that will be felt if reflux occurs. Large meals increase the distension that leads to transient LES relaxations, and eating before bedtime eliminates the effect of gravity before the stomach empties.

Smoking

Smoke directly causes LES muscle relaxation, induces a cough that repeatedly opens the valve, delays gastric emptying, and decreases salivary secretions, which are the body's natural buffers for stomach acid in the esophagus. Smokers are more likely to develop hiatal hernias than non-smokers, probably from strain on their diaphragms from prolonged coughing.

Pregnancy

Pregnancy leads to transient GERD in most women through two mechanisms: increased intra-abdominal pressure due to the growing uterus and the relaxing effect of progesterone and relaxin on smooth muscle tissue, including the LES.

Medications and Other Conditions

Several drugs have the side effect of lowering the LES pressure. These are calcium channel blockers, nitrates, benzodiazepines, asthma inhalers, and tricyclic antidepressants. NSAIDs do not reduce the pressure in the esophagus; rather, they irritate the esophageal lining. In gastroparesis, which is diabetes-induced stomach emptying, the stomach acid lingers in the stomach, thereby increasing the risk of heartburn. Connective tissue diseases, such as scleroderma, lead to motility disorders in the esophagus.

Conclusion

When GERD occurs, it is the result of the breakdown in the stomach's "containment system" due to a weakened LES, a hiatal hernia that has moved, pressure on the stomach, or the relaxing effect of chemicals on the valve. What makes GERD chronic in most cases is an anatomical abnormality, such as a hiatal hernia or obesity, that prevents the "containment system" from functioning normally. The difference between treating the symptoms and treating the disease is understanding the underlying elements in each case. Frequent heartburn or regurgitation should be taken seriously.

Frequently Asked Questions

Can stress cause GERD?

Not directly, but it makes symptoms feel worse and leads to behaviors that trigger reflux, such as overeating, smoking, and drinking. Some studies indicate that stress makes the esophagus more sensitive to stomach acid.

Is GERD always caused by too much stomach acid?

No. Most people with GERD produce normal acid levels; the problem is acid reaching the esophagus, where it does not belong. Some people also reflux bile or non-acidic contents.

Can GERD go away on its own?

Occasional reflux may be treated by changing one's lifestyle. GERD that is chronic may require continued management, except in those instances where a causative factor, such as obesity, is treated. GERD that is pregnancy-related usually goes away after delivery.

Which medications are most likely to worsen GERD?

Calcium channel blockers, nitrates, benzodiazepines, NSAIDs, and some asthma medications are common culprits. Discuss other treatment options with your doctor rather than stopping them without guidance.

Does eating late at night cause GERD?

One of the known triggers is eating close to bedtime. When one goes to sleep, gravity is no longer able to hold down the contents of the stomach, and this risk is heightened when one has a full or distended stomach.

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