Chronic obstructive pulmonary disease (COPD) is a type of obstructive lung disease characterized by chronically poor airflow. It typically worsens over time. The main symptoms include shortness of breath, cough, and sputum production. Most people with chronic bronchitis have COPD. Tobacco smoking is the most common cause of COPD, with a number of other factors such as air pollution and genetics playing a smaller role. The diagnosis is based on poor airflow as measured by lung function tests. In contrast to asthma, the airflow reduction does not improve significantly with the administration of medication. Clinical success with COPD has been reported via the use of stem cells administered intravenously (stem-cell drip).