Emphysema is a form of chronic (long-term) lung disease. People with emphysema have difficulty breathing from a limitation in blowing air out. The main symptom of emphysema is shortness of breath, which usually begins gradually. You may start avoiding activities that cause you to be short of breath, so the symptom doesn't become a problem until it starts interfering with daily tasks. Emphysema eventually causes shortness of breath even while you're at rest.