Phlegm and filters.

Male mass radiography volunteers aged 40 or more were questioned about their sputum production and cigarette consumption in relation to type (filter or plain) smoked. Of 10,414 volunteers, 3,045 smoked filter cigarettes and 2,393 smoked plain cigarettes. The rate of persistent daily sputum of filter smokers (31.9%) was significantly lower than that of plain cigarette smokers (37.2%). A similar pattern was maintained when age and cigarette consumption were standardized. These figures are thought to understate the less injurious nature of filter cigarettes, since more than half of the filter smokers with persistent sputum developed this while previously smoking plain cigarettes.Whatever the reasons for the less injurious nature of filter cigarettes, it seems that cigarette smokers unable to stop smoking might suffer less from chronic bronchitis if they changed to filter cigarettes.