Esophagitis can be caused by infection or irritation of the esophagus. Infections of the esophagus can be caused by bacteria, viruses, or fungi, including:
Candida, a yeast infection. This is more common in patients with weakened immune systems, such as those with diabetes, HIV/AIDS, patients undergoing chemotherapy, or people who are taking antibiotics or steroids.
Herpes, a viral infection. It may develop in the esophagus when the body's immune system is weak.

One of the main causes of esophageal irritation is reflux of stomach acid. There are several causes for reflux:
GERD (gastroesophageal reflux disease): weakness or dysfunction of the muscle that keeps the stomach closed (sphincter) can allow stomach acid to leak into the esophagus (acid reflux), causing irritation of the inner lining. Also called GERD esophagitis - in severe cases it can become erosive esophagitis (this also may be referred to as ulcerative esophagitis).

Vomiting: when vomiting is frequent or chronic it can lead to acid damage to the esophagus. Excessive or forceful vomiting may cause small tears of the inner lining of the esophagus, leading to further damage.

Hiatal hernia: This abnormality occurs when a part of the stomach moves above the diaphragm producing a small abnormal pouch, or hiatal hernia, which can lead to excess acid refluxing into the esophagus.

Achalasia: This is a disorder where the lower end of the esophagus does not open normally, and as a result food can get stuck in the esophagus or is regurgitated. People with achalasia have a higher than normal risk of esophageal cancer.