Epidemiology of bronchial hypersecretion: recent studies.

The predominant cause of mucus hypersecretion in Westernized countries is smoking. Mucus hypersecretion in smokers is correlated with the subsequent development of bronchial carcinoma but there is no definite causal relation to progressive airflow obstruction. The distinction between hypersecretion and the development of airflow obstruction may also be relevant in childhood and occupational respiratory disease. Endogenous factors may also be important, as suggested by the increased prevalence of hypersecretion in asthma, but are difficult to detect by epidemiological techniques.