Smoking Definitions and Health Implications

Clinical Definitions Based on Smoking Status

The American College of Cardiology defines a current everyday user as a person who reports currently smoking tobacco every day and has smoked at least 100 cigarettes (5 packs) in their lifetime 1, 2
The American College of Cardiology defines a former user as a person who does not currently smoke tobacco but has smoked at least 100 cigarettes in their lifetime, with long-term abstinence often defined as 6 months of abstinence 1, 2
The American College of Cardiology defines a never user as a person who has not smoked tobacco regularly and does not now smoke every day or some days; defined as an individual who has not smoked 100 cigarettes (5 packs) in their lifetime 1, 2

The standard measurement for quantifying lifetime tobacco exposure is pack-years, with one pack-year defined as smoking 20 cigarettes per day for 1 year 1, 2
Pack-years are critical for assessing long-term health risks 3

A 20 pack-year smoking history is an important threshold used in lung cancer screening guidelines, with individuals at this level eligible for screening 3
Former smokers with more than 20 pack-years have a 3.06-fold increased risk of lung cancer mortality compared to never smokers 3

Chronic smokers have significantly higher risks of all-cause mortality, with risk persisting even after cessation 3
Former smokers with >20 pack-years still have a 2.20-fold increased risk of lung cancer mortality even after 25 years of smoking cessation 3
Smoking is the single most important cause of COPD, with risk directly proportional to tobacco exposure 4