In the 1950's and 60's, the tobacco industry mounted a campaign to keep alive the doubt of the time about the consequences of smoking. This effort ultimately was unsuccessful but did however succeed in putting off the day when smoking was finally acknowledged as a health hazard. The tobacco industry also foresaw the health debate over secondhand smoke in the 1970's. Secondhand smoke is a combination of the smoke from a burning cigarette and the smoke exhaled by the smoker. This smoke, often referred to as Environmental Tobacco Smoke (ETS), is recognized easily by its odor. ETS contaminates the air and is held in fabrics such as clothing and furniture. In an U.S. Environmental Protection Agency (EPA) report in December 1992 entitled "Respiratory health Effects of Passive Smoking", the EPA classified environmental tobacco smoke a Class A human carcinogen, causing cancer in humans and unsafe at any level. The EPA firmly maintains that the bulk of the scientific evidence demonstrates that ETS causes lung cancer and other significant health threats to children and adults. Since the EPA's initial findings, it has become widely accepted in the scientific and public health community that secondhand smoke poses a significant health risk.
The tobacco industry, in an attempt to create its own sort of credible medical evidence, commissioned research from sympathetic scientists, sponsored scientific meetings tailored to bring out their point of view, and published their own results. The heart of the tobacco industry's campaign appears to be their attack on the scientific methods used to measure the risk of secondhand smoke. The tobacco industry currently seems to not be trying to completely rebuke the effects of secondhand smoke, but appear to be trying to downplay the evidence. The University of California, San Francisco has documented the results of research paid for by the tobacco industry between 1974 and 1990.