Asthma, known medically as reactive airway disease, is a chronic lung condition that affects about 20 million Americans, according to the National Heart, Lung, and Blood Institute (NHLBI) at the National Institutes of Health. Symptoms of asthma occur when the airway becomes inflamed and constricts to make breathing difficult. What causes asthma or why incidences of asthma are on the rise is not known, but some have suggested that it could be the result of environmental factors such as an increase in exposure to pollution or indoor allergens. Its increase may also be related to the increase in obesity that is simultaneously occurring. Many researchers are looking for a genetic factor for asthma based on the fact that a person has a higher risk of developing asthma if a member of his or her family has it. Whatever causes asthma, it is a serious and sometimes fatal condition that must be carefully managed.People with asthma often suffer from nighttime coughing, wheezing and breathlessness that disturb their sleep