How does pneumothorax happen for no reason?

Pneumothorax: Folks with copd/emphysema are more prone to get spontaneous pneumothorax.

Happens for a reason: Adolescents & young adults have "spontaneous" pneumothorax more frequently than other folks. The lung tissue usually has a minor congenital defect called a "bleb, " that bursts leading to a leak of air outside the lung - pneumothorax ensues. These folks are usually tall & lean. Of course, trauma can lead to pneumothorax, as can certain illnesses, particularly, marfan's syndrome.

Usually a reason: Risk factors for primary and secondary spontaneous pneumothorax (sp) include: smoking (including marijuana), tall thin stature in otherwise healthy, connective tissue disorders, pregnancy, familial history. Lung inflammation is also hypothesized to be important.