The link between allergic rhinitis and asthma: the united airways disease.

Rhinitis and asthma are often associated and the two disorders interact at various levels. Rhinitis typically precedes the development of asthma and can contribute to unsatisfactory asthma control. The presence and type of asthma is influenced by sensitization, and the duration and severity of allergic rhinitis. Nasal symptoms, airflow and markers of inflammation directly correlate with lower airway involvement. Local tissue factors, such as microbial stimuli and systemic inflammatory mechanisms, play a role in the clinical expression of the allergic airway syndrome. There is increasing evidence that suggests a major involvement of airway epithelial cells in the pathogenesis of both asthma and allergic rhinitis. Even in patients with rhinitis who do not have asthma, subclinical changes in the lower airways and inflammatory mediators can be detected. The pathogenic role of paranasal sinus infections in respiratory allergy has been better elucidated but there remains a need for further research. Treatment of established rhinitis may affect asthma control and could have some impact on airway obstruction, but a direct effect of rhinitis therapy on lower airway inflammation remains to be clearly established.