Asthma Overview Make an Appointment Find a Doctor Ask a Question Reviewed by David Tinkelman, MD (April 01, 2012) Asthma is a chronic respiratory disease. It is sometimes worrisome and inconvenient, but a manageable condition. It is also known as reactive airway disease. With proper understanding, good medical care and monitoring, you can keep asthma under control. If you have asthma, you are not alone. In the United States, asthma affects 14 to 15 million people. Asthma is defined as a chronic lung condition with inflammation (swelling) of the airways, increased sensitivity of the airways to a variety of things that make asthma worse and obstruction of airflow. There are various types of asthma, including: Exercise-induced asthma Nocturnal asthma Occupational asthma Steroid-resistant asthma Allergic asthma Typical Changes in the Airway Inflammation Recent research has shown that inflammation of the lining of the airways is the most common feature of asthma. When they are stimulated, certain cells lining the airways release chemical substances (mediators) that lead to inflammation. This causes the airway lining to swell and narrow. The inflammation may last for hours, days or weeks following an episode. Most people with asthma have some degree of inflammation all of the time. Some long-term control medications can help prevent and reduce inflammation. Increased Sensitivity Another characteristic of asthma is increased sensitivity of the airways. When inflammation occurs in the airways, the airways become more sensitive (or "twitchy"). When the airways are more sensitive, you are more likely to have asthma symptoms when exposed to things that can make asthma worse. The more sensitive your airways, the less it takes to cause a problem. When there is less inflammation, the airways are less sensitive, and you are less likely to have asthma symptoms when exposed to things that make asthma worse. Airway Obstruction In addition to the swelling that occurs as a result of inflammation, further airway obstruction sometimes occurs with asthma. Obstruction is caused by tightening of muscles that surround the airways. This is also called bronchospasm. Bronchospasm causes further narrowing of the inflamed airways. Inhaled quick-relief medications are generally very effective in reversing bronchospasm. In most people with asthma, the mucus glands in the airways produce excessive, thick mucus, which further obstructs the airways and causes coughing. Programs & Services Deployment-Related Lung Disease Center The Cohen Family Asthma Institute Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.