Asthma is a common disease, whose prevalence has been increasing worldwide. Asthma is a chronic inflammatory disease of the airways, with airway eosinophils being the most prominent inflammatory cell. A number of initiating factors have been identified, including environmental allergens, viral infections, and volatile molecules and allergens in the workplace. Variable airflow obstruction and airway hyperresponsiveness are the physiological hallmarks of asthma and a variety of stimuli, such as exercise, atmospheric pollutants, and strong smells, can induce airflow obstruction and symptoms in asthmatic patients. Inhaled corticosteroids are the mainstay of treatment of persistent asthma and these medications in combinations with long-acting inhaled β2-agonists are effective in many patients if inhaled corticosteroids are not providing optimal asthma control.