Lung diseases are some of the most common medical conditions in the world. Tens of millions of people have lung disease in the U.S. alone. Smoking, infections, and genes cause most lung diseases. Your lungs are part of a complex system, expanding and relaxing thousands of times each day to bring in oxygen and send out carbon dioxide. Lung disease can happen when there are problems in any part of this system. Your windpipe (trachea) branches into tubes called bronchi, which in turn become smaller tubes throughout your lungs. Diseases that can affect these airways include: In Asthma airways are constantly inflamed and may spasm, causing wheezing and shortness of breath. Allergies, infections, or pollution can trigger asthma symptoms. Chronic (COPD), with this lung condition, you can’t exhale the way you usually would, which causes trouble breathing. In Chronic bronchitis a form of COPD brings a long-term wet cough. In Emphysema. Lung damage allows air to be trapped in your lungs in this form of COPD. Trouble blowing air out is its hallmark. Acute bronchitis cause sudden infection of your airways is usually caused by a virus. Cystic fibrosis. With this condition, you have trouble clearing mucus out of your bronchi. This leads to repeated lung infections.