A sphincter, which is a kind of ’valve’, controls the passage of food from the esophagus to the stomach. It is a bundle of muscle fibres that opens up when food goes from the esophagus to the stomach. Immediately after that, the sphincter closes to prevent the backward flow of gastric juices into the esophagus. In the case of achalasia, this lower esophagus muscle does not work properly: it does not relax sufficiently, so that food remains in the esophagus after swallowing. This is because the nerves that control this sphincter are affected. Another characteristic of achalasia is the lack of the normal rhythmic contractions of the esophagus (wave movements) that propel the food from top to bottom into the esophagus. Probably this is also due to an impairment of the nerves.
Achalasia can occur at any age, but usually starts between 20 and 40 years. It can remain unnoticed for a long time and gradually increase over the years.