Although the exact cause of acid reflux disease differs from person to person, In all cases, the lower esophageal sphincter (LES), which is responsible for keeping stomach contents from flowing back into the esophagus, is open when it should be closed. 

This results in the uncomfortable and frequently painful burning sensation known as heartburn, where stomach acid and digestive enzymes irritate the lining of the esophagus.

Common Causes of GERD:

Abnormal muscle or nerve function: The LES depends on muscle strength to remain closed against the pressure of stomach contents, as well as nerve impulses to tell it when to close tight and when to relax to let food pass through it. Additionally, stomach problems with muscle and nerve function can cause increased pressure because of delayed emptying.

Medications: Many prescription and over-the-counter drugs are known to cause GERD or increase the severity of symptoms. The list of medications is long, but some of the most frequent culprits are:

• Oral contraceptives and hormones: Progesterone-containing medications such as birth control pills and post-menopause hormones.
• Nonsteroidal Anti-Inflammatory drugs (NSAIDs): NSAIDs are a commonly used group of medications for pain control. They include aspirin, ibuprofen (Motrin, Advil, Nuprin), and naproxen (Aleve).
• Calcium channel blockers: Used to treat high blood pressure and angina.
• Anticholinergics: These are used in drugs that treat urinary tract disorders, allergies, and glaucoma.
• Beta-adrenergic agonists: These are used in drugs for asthma and obstructive lung diseases.
• Dopamine: This is used to reduce symptoms of Parkinson’s disease.
• Bisphosphonates: Used to treat osteoporosis.
• Sedatives, antibiotics, potassium, iron pills, corticosteroids, and vitamin supplements

Asthma: Although there is some question over which condition, asthma or GERD, occurs first and causes the other, a large number of people living with asthma have GERD and vice versa. The coughing common in asthma attacks raises abdominal pressure and causes reflux. It is also possible that chronic reflux of acid irritates the windpipe and results in upper respiratory problems like asthma.

Pregnancy: During pregnancy, increased abdominal pressure as the baby grows, along with increased levels of hormones that relax the LES muscles, contribute to heartburn.

Diabetes: Some people with diabetes develop a condition that slows stomach emptying. This condition, called gastroparesis, increases stomach pressure and, in turn, increases the chances of reflux.

Hiatal Hernia: As it travels from the mouth to the stomach, the esophagus passes through a layer of muscle called the diaphragm, which separates the lung cavity from the lower abdomen and helps with breathing.  The hole through the diaphragm can sometimes become large enough for part of the stomach to bulge through it. This changes the angle at which the esophagus joins the stomach, weakens the ligaments holding the stomach and esophagus in place, and prevents the LES from working correctly. Surgical repair of hiatal hernias is often required.

Food and drink: People react differently to the foods they eat, making defining a list of foods that cause or worsen GERD difficult.  Some of the more common problems with foods and drinks are:

• Alcohol: irritates the esophagus and  loosens the LES
• Caffeine: Coffee and other caffeine-containing drinks stimulate stomach acid production
• Chocolate: relaxes the LED
• Mint: relaxes the LED
• Fried and fatty foods
• Spicy foods and acidic foods

Lifestyle: Eating too quickly, skipping meals and then eating a large meal to make up for it, exercising, or lying down after eating all contribute to the possibility of reflux.

Smoking: The irritant effect of smoke is the tendency to swallow air while smoking and increased stomach pressure can cause reflux.