GERD occurs when stomach contents repeatedly flow back into the esophagus. The main causes are a weak lower esophageal sphincter (often linked to a hiatal hernia), excess acid or bile, slow gastric emptying, and impaired clearing by swallowing or saliva. Nocturnal reflux worsens due to lying flat and reduced saliva. Lifestyle factors such as obesity, smoking, and certain foods contribute. See a clinician for frequent or severe symptoms to prevent complications.
What is acid reflux (GERD)?
Acid reflux happens when stomach contents flow back into the esophagus. Occasional reflux is common. When symptoms are frequent or cause damage to the esophagus, clinicians call it gastroesophageal reflux disease (GERD).
What usually causes reflux
Lower esophageal sphincter (LES) dysfunction
The most common mechanical reason is a weak or relaxed lower esophageal sphincter (LES) - the valve between the esophagus and stomach. If the LES does not close properly, stomach contents can move upward.
A hiatal hernia can make LES dysfunction more likely. In a hiatal hernia a portion of the stomach moves through the diaphragm and changes the anatomy that helps keep the LES closed.
Too much acid or bile
Refluxed fluid is usually acidic because of stomach acid. In some people bile (from the small intestine) also refluxes and can irritate the esophagus. Both acid and bile can cause heartburn, regurgitation, and a sour or bitter taste.
Delayed stomach emptying and increased pressure
If the stomach empties slowly, or if pressure inside the abdomen rises (for example with obesity or after large meals), reflux becomes more likely. Certain medications can also relax the LES or slow gastric emptying.
Swallowing and saliva
Swallowing triggers esophageal muscle contractions that clear refluxed material. Saliva helps neutralize acid and coats the esophagus. If swallowing is impaired or saliva production is reduced (for example during sleep), clearance is less effective and symptoms can worsen.
Why reflux often gets worse at night
Two main factors make nocturnal reflux common: lying flat removes the benefit of gravity that helps keep stomach contents down, and saliva production falls during sleep so less neutralization and clearing occur. Nighttime reflux often causes coughing, sore throat, or sleep disruption.
Common triggers and contributing factors
Lifestyle and medical factors that increase reflux include overeating, certain foods and drinks (spicy foods, citrus, caffeine, alcohol), smoking, obesity, and pregnancy. Pregnancy-related reflux is usually due to hormonal changes and increased abdominal pressure; many women improve after delivery.
When to see a clinician
Occasional heartburn can be managed with lifestyle changes and over-the-counter antacids. Seek medical evaluation for frequent or severe symptoms, difficulty swallowing, unintended weight loss, vomiting, or any signs of gastrointestinal bleeding. Persistent GERD can damage the esophagus and may require testing and targeted treatment.
Bottom line
Reflux has multiple causes: valve (LES) problems, hiatal hernia, excess acid or bile, delayed gastric emptying, reduced clearance by swallowing/saliva, and lifestyle factors. Understanding the likely cause helps guide treatment and when to seek medical care.