A pneumothorax occurs when some of the tiny air sacs (alveoli) in a baby's lung become overinflated and burst. This causes air to leak into the space between the lung and chest wall (pleural space).
The most common cause of pneumothorax is respiratory distress syndrome. This is a condition that occurs in babies who are born too early (premature).
The baby's lungs lack the slippery substance (surfactant) that helps them stay open. Therefore, the tiny air sacs are not able to expand as easily.
If the baby is put on a breathing machine (mechanical ventilator), there is extra pressure on the baby's lungs, which can sometimes burst the air sacs.