What is the cause of asthma?
At a basic level the cause of asthma is unknown. Given an individual’s predisposition to asthma, a variety of factors can trigger symptoms (Table 1). Perhaps the most common trigger in adults is respiratory viral infections, including the common cold. Less common, but very important, are allergens, substances that when inhaled can react with the host’s antibodies to generate an allergic response. Allergens include various plant pollens, animal furs, excreta from house mites, proteins in shellfish, and some metals. Allergens play a major role in many cases of occupational asthma. Irritants can also trigger an asthma attack through a non-allergic mechanism, by directly injuring cells within the lungs. Other triggers of an asthma attack include climate changes; exercise, particularly in cold weather; certain medications such as aspirin; and acid-reflux from the stomach. Although everyone is subjected to the types of triggers listed in Table 1, only the 5-10 percent of the population with
