Sex In general, men are far more likely to have a pneumothorax than are women.
Smoking The risk increases with the length of time and the number of cigarettes smoked, even without emphysema.
Age The type of pneumothorax caused by ruptured air blisters (sub-pleural blebs) is most likely to occur in young individuals between 20 and 40 years old, especially if the person is a very tall and underweight man.
Genetics Certain types of pneumothorax appear to run in families.
Lung disease Certain underlying lung disease - especially emphysema, pulmonary fibrosis, sarcoidosis, and cystic fibrosis - makes a person more susceptible to pneumothorax and collapsed lung.
Mechanical ventilation Critical patients who need mechanical ventilation to breathe effectively are at higher risk of pneumothorax.
A history of pneumothorax Anyone who has had one pneumothorax is at increased risk of another, usually within one to two years of the first episode. This may occur in the same lung or the opposite lung.