Smoking, asthma, chronic airflow obstruction and COPD.

Cigarette smoking is the most prevalent risk factor for the development of adult-onset respiratory diseases associated with airflow obstruction, namely emphysema and chronic bronchitis, commonly called chronic obstructive pulmonary disease (COPD). Regrettably, childhood asthma does not reduce the likelihood of initiation of smoking [1] but it is not fully clear how smoking impacts pre-existing airway diseases such as asthma. Does smoking worsen asthma or superimpose another disease? How does asthma itself, irrespective of smoking, impact lung function in adulthood? What characteristics of asthma increase the risk of smoking-induced worsening of airflow obstruction? Does asthma lead to COPD?