Achalasia is a medical condition that affects the oesophagus, the tube that carries food from the mouth to the stomach. It is a rare disorder characterized by the inability of the lower oesophageal sphincter (LES) to relax and allow food to pass into the stomach. This lack of relaxation is caused by the degeneration of the nerves in the oesophageal muscles. The exact cause of achalasia is unknown, although it is thought to be related to an autoimmune response that damages the nerves controlling the lower oesophageal sphincter. (LES). In rare cases, achalasia may be associated with certain autoimmune disorders or infections