Asthma is a chronic disease that affects the airways of the respiratory system. In the United States, about 20 million people have been diagnosed with asthma, nearly half of those affected being children. The incidence of asthma is rising in developed countries, though there is great variation in incidence between countries and socioeconomic groups.
Episodes of asthma are characterized by a constriction of the airways, as the airways become inflamed and excessive amounts of mucus line the airways. Due to the narrowing of reactive airways, less air is able to flow to the lungs. This can result in wheezing, coughing, chest tightness, and trouble breathing, especially at night and in the early morning. The exact triggers for asthma are not clear-cut. Moreover, triggers may be due to a combination of factors. Recognized triggers include allergens (e.g. animal dander, dust mites, pollen, and mold), irritants (e.g. cigarette smoke, air pollution, cold air or changes in weather, strong odors such as those from painting or cooking, scented products or perfumes, moist air, exercise or exertion, or emotional stress), or other factors such as certain medicines (e.g. aspirin and beta-blockers), sulfites in food (dried fruit) or beverages (wine), gastroesophageal reflux, and infections. In children, the most common triggers are viral illnesses such as those that cause the common cold. The disease also has a significant genetic component.
The development of asthma involves many genes and environmental factors. An understanding of the genetic basis of the disease has great implications its management. To date, dozens of genes have been associated with asthma. Many of the genes are related to the immune system or to modulating inflammation. However, results have not been consistent among various populations studied, indicating that there is variation in the disease and not all genes are associated with asthma under every condition. The heterogeneity in the disease highlights the complex interactions causing the disease and the need for further study to fully understand the mechanisms involved.
The symptoms of asthma can range from mild to life threatening. Symptoms can usually be controlled with a combination of drugs and environmental changes. Treatment for asthma includes avoiding triggers, such as allergens and irritants, monitoring asthma and associated symptoms, and asthma medicines. Current asthma medicines include beta-agonists (bronchodilators), corticosteroids, theophylline and leukotriene modifiers.