Blebs. Non-trauma, spontaneous pneumothorax occur as a result of an abnormality in the lung tissue. 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. In short, if you are healthy, non-smoker, you may just have abnormality in your lungs (blebs).
Bad break. Collapsed lung, or pneumothorax is usually the result of external trauma - car accidents and other causes of I jury. Once in a while, a patient will get a spontaneous pneumothorax. This can be painful and scary. Sometimes there is an identified - and almost always benign - underlying lung abnormality. Sometimes various treatments will be required.