Asthma is a common inflammatory disease that affects the airways, causing them to become swollen and sensitive to inhaled substances and irritants. The symptoms of asthma can range from mild to very severe and include wheezing and breathlessness. For many asthma sufferers airway inflammation can be controlled effectively with inhaled anti-inflammatory drugs, however, for others their asthma remains poorly controlled despite maximum inhaled treatment. For these people identification and control of trigger factors for asthma may help in achieving asthma control.