Emphysema is a condition in which the bronchial tubes and lungs become damaged over time, resulting in shortness of breath. Smoking is nearly always the main cause of emphysema. Emphysema usually does not develop until people are in their 50s or 60s. An accelerated form of emphysema has been reported in some young persons infected with the human immunodeficiency virus (HIV), which is the virus that causes AIDS. However, those reports did not compare persons infected with HIV directly with persons without HIV infection.