Chalasia is the abnormal relaxation or incompetence of the lower oesophageal sphincter, allowing stomach contents to reflux into the oesophagus. The term is used particularly for the condition in infants, where an immature sphincter causes frequent vomiting and poor weight gain, though most outgrow it as the valve strengthens. In adults the equivalent problem is usually called gastro-oesophageal reflux disease. Dietary management includes small, frequent feeds, upright positioning after meals, and thickened feeds for infants on medical advice. Persistent cases need investigation to exclude anatomical causes, and nutrition support ensures growth continues despite the losses.