There have been few epidemics as devastating and preventable as that caused by tobacco consumption. Cigarette smoking and exposure to secondhand smoke (SHS) became highly prevalent in most developed countries through the 20th century; with a lag of several decades, the rise of smoking was followed by epidemic increases in the diseases now known to be caused by smoking, including lung and other cancers, coronary heart disease, and chronic lung disease. By mid-century, epidemiologic studies provided the initial evidence establishing that smoking caused these diseases. Mounting evidence and authoritative syntheses in the reports of the United States (US) Surgeon General soon led to definitive conclusions concerning smoking as a cause of disease. Unfortunately, as the 21st century begins, smoking is on the rise in developing countries, even as it declines in the developed countries that have had some success with tobacco control.
This topic will focus on the health consequences of SHS in adults. Issues related to SHS exposure to a fetus/child and effects of active cigarette smoking are discussed separately. (See "Secondhand smoke exposure: Effects in children" and "Cardiovascular risk of smoking and benefits of smoking cessation".)
The issue of SHS and health has a relatively brief history compared to active smoking, although the irritating nature of tobacco smoke to the nonsmoker has long been chronicled. Some of the first epidemiological studies on SHS and health were reported in the late 1960s [1-3]; there had been scattered case reports previously, and there were campaigns against smoking in public in Nazi Germany. One German physician, Fritz Lickint, used the term "passive smoking" in his 1939 book on smoking . The 2006 Surgeon General's report uses the term "secondhand smoke," although the term "environmental tobacco smoke" (ETS), originating within the tobacco industry, was used more frequently in earlier reports and discussions on the topic .
Initial epidemiological investigations focused upon parental smoking and lower respiratory illnesses in infants; studies of lung function and respiratory symptoms in children soon followed [6,7]. The first major studies on SHS smoke and lung cancer in nonsmokers were reported in 1981 [8,9], and by 1986 the evidence supported the conclusion that SHS was a cause of lung cancer in nonsmokers, a conclusion reached by the International Agency for Research on Cancer (IARC), the US Surgeon General, and the US National Research Council [7,10,11]. Subsequently, a now substantial body of evidence has continued to identify new diseases and other adverse effects of SHS, including increased risk for coronary heart disease [6,12-15].
The 2006 US Surgeon General's Report leaves no doubt that any exposure to tobacco smoke is harmful to human health . The findings on SHS and disease have been the foundation of the drive for smoke-free indoor environments and for educating parents concerning the effects of their smoking on their children's health. As bans are implemented, an increasing body of evidence documents reduction of exposure and benefits for cardiovascular and respiratory health.