One of the main reasons that people experience the caustic fluid backup that is characteristic of acid reflux is improper functioning of the lower esophageal sphincter, or LES muscles. These muscles are found at the base of the esophagus and provide a method of opening and closing the passageway to the stomach. When the LES muscles are weakened, they are often unable to fully close. This can result in acid from the stomach finding its way up into the esophagus.

Abnormalities in the esophagus are another common cause. Several parts of the esophagus can be malformed, but the two most common ones are peristalsis and what is known as adult-ringed esophagus. Adult-ringed esophagus is a condition with small rings in the throat that stop a person from swallowing properly. Improper stomach function is yet another factor that can lead to acid reflux disease.

Over half of the people suffering with acid reflux have stomach muscles that are not able to respond quickly to stimuli. This can lead to extended time periods when the stomach is not emptied, which can in turn lead to a backing up of acid into the esophagus.

Hiatal hernias are another common problem. The hiatus is a hole in the diaphragm that helps to keep the passageway between the stomach and the esophagus secure. It's normally tight, but if it becomes weakened somehow the muscles can loosen and lead to a small part of the stomach actually protruding through the hiatus.

This condition is known as a hiatus hernia. These hernias are not responsible for acid reflux directly, but they can cause the LES muscles to not function properly, ultimately leading to reflux problems.

On top of all the previous causes, certain drugs can also play a part. Non-steroidal anti-inflammatory drugs (NSAIDs) can sometimes lead to acid reflux, as well as aggravating the condition in people who already have it.

These are common drugs and are in a number of well-known brands such as Motrin, Advil, Aleve, and Nuprin. A recent study showed that people who were taking these drugs had twice as much chance of experience at least some symptoms of acid reflux disease.

Asthma and diabetes are two other things to consider when diagnosing the cause of acid reflux. At least half of all asthma sufferers are known to experience acid reflux, and we have not yet discovered which disease may be causing the other.

Diabetes sufferers need to be wary of their eating habits when it comes to acid reflux; many diabetics suffer from gastroparesis, a condition that causes a delay in the emptying of the stomach. This can cause a backup in the stomach and consequently an acid buildup in the esophagus.