Passive smoking is the inhalation of smoke, called secondhand smoke (SHS) or environmental tobacco smoke (ETS), from tobacco products used by others. It occurs when tobacco smoke permeates any environment, causing its inhalation by people within that environment. Exposure to secondhand tobacco smoke causes disease, disability, and death. Currently, the health risks of secondhand smoke are a matter of scientific consensus. These risks have been a major motivation for smoking bans in workplaces and indoor public places, including restaurants, bars and night clubs, as well as some open public spaces.
Secondhand smoke causes many of the same diseases as direct smoking, including cardiovascular diseases, lung cancer, and respiratory diseases. These diseases include:
- Cancer:
- General: overall increased risk; reviewing the evidence accumulated on a worldwide basis, the International Agency for Research on Cancer concluded in 2004 that "Involuntary smoking (exposure to secondhand or 'environmental' tobacco smoke) is carcinogenic to humans."
- Lung cancer: the effect of passive smoking on lung cancer has been extensively studied. A series of studies from the USA from 1986–2003, the UK in 1998 primarily premenopausal women by 70% and the US Surgeon General has concluded that the evidence is "suggestive," but still insufficient to assert such a causal relationship. In contrast even if the mother doesn't smoke, thus not restricting risk to prenatal exposure during pregnancy.
Epidemiological studies show that non-smokers exposed to secondhand smoke are at risk for many of the health problems associated with direct smoking.
The International Agency for Research on Cancer of the World Health Organization concluded in 2004 that there was sufficient evidence that secondhand smoke caused cancer in humans. Most experts believe that moderate, occasional exposure to secondhand smoke presents a small but measurable cancer risk to nonsmokers. The overall risk depends on the effective dose received over time. The risk level is higher if non-smokers spend many hours in an environment where cigarette smoke is widespread, such as a business where many employees or patrons are smoking throughout the day, or a residential care facility where residents smoke freely. The US Surgeon General, in his 2006 report, estimated that living or working in a place where smoking is permitted increases the non-smokers' risk of developing heart disease by 25–30% and lung cancer by 20–30%.
Environmental tobacco smoke can be evaluated either by directly measuring tobacco smoke pollutants found in the air or by using biomarkers, an indirect measure of exposure. Carbon monoxide monitored through breath, nicotine, cotinine, thiocyanates, and proteins are the most specific biological markers of tobacco smoke exposure. Biochemical tests are a much more reliable biomarker of environmental tobacco smoke than surveys. Certain groups of people are reluctant to disclose their smoking status and exposure to tobacco smoke, especially pregnant women and parents of young children. This is due to their smoking being socially unacceptable. Also, it may be difficult for individuals to recall their exposure to tobacco smoke.
Cotinine, the metabolite of nicotine, is a biomarker of environmental tobacco smoke exposure. Typically, cotinine is measured in the blood, saliva, and urine. Hair analysis has recently become a new, noninvasive measurement technique. Cotinine accumulates in hair during hair growth, which results in a measure of long-term, cumulative exposure to tobacco smoke. Urinary cotinine levels have been a reliable biomarker of tobacco exposure and have been used as a reference in many epidemiological studies. However, cotinine levels found in the urine only reflect exposure over the preceding 48 hours. Cotinine levels of the skin, such as the hair and nails, reflect tobacco exposure over the previous three months and are a more reliable biomarker.
Carbon monoxide monitored via breath is also a reliable biomarker of environmental tobacco smoke exposure as well as tobacco use. With high sensitivity and specificity, it not only provides an accurate measure, but the test is also non-invasive, highly reproducible, and low in cost. Breath CO monitoring measures the concentration of CO in an exhalation in parts per million, and this can be directly correlated to the blood CO concentration (carboxyhemoglobin). Breath CO monitors can also be used by emergency services to identify patients who are suspected of having CO poisoning.
A 2004 study by the International Agency for Research on Cancer of the World Health Organization concluded that nonsmokers are exposed to the same carcinogens as active smokers. Sidestream smoke contains more than 4,000 chemicals, including 69 known carcinogens. Of special concern are polynuclear aromatic hydrocarbons, tobacco-specific N-nitrosamines, and aromatic amines, such as 4-aminobiphenyl, all known to be highly carcinogenic. Mainstream smoke, sidestream smoke, and secondhand smoke contain largely the same components, however the concentration varies depending on type of smoke. Several well-established carcinogens have been shown by the tobacco companies' own research to be present at higher concentrations in sidestream smoke than in mainstream smoke.
There is widespread scientific consensus that exposure to secondhand smoke is harmful. The link between passive smoking and health risks is accepted by every major medical and scientific organization, including:
- The World Health Organization: The governments of 168 nations have signed and currently 174 have ratified the World Health Organization Framework Convention on Tobacco Control, which states that "Parties recognize that scientific evidence has unequivocally established that exposure to tobacco smoke causes death, disease and disability."
- The U.S. National Institutes of Health
- The Centers for Disease Control
- The United States Surgeon General
- The U.S. National Cancer Institute
- The United States Environmental Protection Agency
- The California Environmental Protection Agency
- The American Heart Association, American Lung Association, and American Cancer Society
- The American Medical Association
- The American Academy of Pediatrics
- The Australian National Health and Medical Research Council
- The United Kingdom Scientific Committee on Tobacco and Health
Recent major surveys conducted by the U.S. National Cancer Institute and Centers for Disease Control have found widespread public belief that secondhand smoke is harmful. In both 1992 and 2000 surveys, more than 80% of respondents agreed with the statement that secondhand smoke was harmful. A 2001 study found that 95% of adults agreed that secondhand smoke was harmful to children, and 96% considered tobacco-industry claims that secondhand smoke was not harmful to be untruthful.
As part of its attempt to prevent or delay tighter regulation of smoking, the tobacco industry funded a number of scientific studies and, where the results cast doubt on the risks associated with passive smoking, sought wide publicity for those results. The industry also funded libertarian and conservative think tanks, such as the Cato Institute in the United States and the Institute of Public Affairs in Australia which criticised both scientific research on passive smoking and policy proposals to restrict smoking. New Scientist and the European Journal of Public Health have identified these industry-wide coordinated activities as one of the earliest expressions of corporate denialism. Further, they state that the disinformation spread by the tobacco industry has created a tobacco denialism movement, sharing many characteristics of other forms of denialism, such as HIV-AIDS denialism.
A 2003 study by Enstrom and Kabat, published in the British Medical Journal, argued that the harms of passive smoking had been overstated. Their analysis reported no statistically significant relationship between passive smoking and lung cancer, though the accompanying editorial noted that "they may overemphasise the negative nature of their findings." This paper was widely promoted by the tobacco industry as evidence that the harms of passive smoking were unproven. The American Cancer Society (ACS), whose database Enstrom and Kabat used to compile their data, criticized the paper as "neither reliable nor independent", stating that scientists at the ACS had repeatedly pointed out serious flaws in Enstrom and Kabat's methodology prior to publication. Notably, the study had failed to identify a comparison group of "unexposed" persons.
Gio Batta Gori, a tobacco industry spokesman and consultant and an expert on risk utility and scientific research, wrote in the libertarian Cato Institute's journal Regulation that "...of the 75 published studies of ETS and lung cancer, some 70 percent did not report statistically significant differences of risk and are moot. Roughly 17 percent claim an increased risk and 13 percent imply a reduction of risk."
Steven Milloy, the "junk science" commentator for Fox News and a former Philip Morris consultant, claimed that "...of the 37 studies [on passive smoking], only 7 – less than 19 percent – reported statistically significant increases in lung cancer incidence."
A 1998 report by the International Agency for Research on Cancer (IARC) on environmental tobacco smoke (ETS) found "weak evidence of a dose-response relationship between risk of lung cancer and exposure to spousal and workplace ETS."
In 1993, the United States Environmental Protection Agency (EPA) issued a report estimating that 3,000 lung cancer related deaths in the United States were caused by passive smoking annually.
The tobacco industry's role in funding scientific research on passive smoking has been controversial. A review of published studies found that tobacco-industry affiliation was strongly correlated with findings exonerating passive smoking; researchers affiliated with the tobacco industry were 88 times more likely than independent researchers to conclude that passive smoking was not harmful. In a specific example which came to light with the release of tobacco-industry documents, Philip Morris executives successfully encouraged an author to revise his industry-funded review article to downplay the role of secondhand smoke in sudden infant death syndrome. The 2006 U.S. Surgeon General's report criticized the tobacco industry's role in the scientific debate.
The passive smoking issue poses a serious economic threat to the tobacco industry. It has broadened the definition of smoking beyond a personal habit to something with a social impact. In a confidential 1978 report, the tobacco industry described increasing public concerns about passive smoking as "the most dangerous development to the viability of the tobacco industry that has yet occurred." In United States of America v. Philip Morris et al. , the District Court for the District of Columbia found that the tobacco industry "... recognized from the mid-1970s forward that the health effects of passive smoking posed a profound threat to industry viability and cigarette profits," and that the industry responded with "efforts to undermine and discredit the scientific consensus that ETS causes disease."
The positions of major tobacco companies on the issue of passive smoking is somewhat varied. In general, tobacco companies have continued to focus on questioning the methodology of studies showing that passive smoking is harmful. Some (such as British American Tobacco and Philip Morris) acknowledge the medical consensus that passive smoking carries health risks, while others continue to assert that the evidence is inconclusive. Imperial Tobacco describes secondhand smoke as "annoying" and "unpleasant", but denies any associated health risks. Several tobacco companies advocate the creation of smoke-free areas within public buildings as an alternative to outright smoking bans.
On September 22, 1999, the U.S. Department of Justice filed a racketeering lawsuit against Philip Morris and other major cigarette manufacturers. Almost 7 years later, on August 17, 2006 U.S. District Court Judge Gladys Kessler found that the Government had proven its case and that the tobacco company defendants had violated the Racketeer Influenced Corrupt Organizations Act (RICO). In particular, Judge Kessler found that PM and other tobacco companies had:
- conspired to minimize, distort and confuse the public about the health hazards of smoking;
- publicly denied, while internally acknowledging, that secondhand tobacco smoke is harmful to nonsmokers, and
- destroyed documents relevant to litigation.
As a consequence of the health risks associated with passive smoking, smoking bans in indoor public places, including restaurants, cafés, and nightclubs have been introduced in a number of jurisdictions, at national or local level, as well as some outdoor open areas. 1 Ireland was the first country in the world to institute an outright national ban on smoking in all indoor workplaces on 29 March 2004. Since then, many others have followed suit. The countries which have ratified the WHO Framework Convention on Tobacco Control (FCTC) have a legal obligation to implement effective legislation "for protection from exposure to tobacco smoke in indoor workplaces, public transport, indoor public places and, as appropriate, other public places." (Article 8 of the FCTC) The parties to the FCTC have further adopted Guidelines on the Protection from Exposure to Secondhand Smoke which state that "effective measures to provide protection from exposure to tobacco smoke ... require the total elimination of smoking and tobacco smoke in a particular space or environment in order to create a 100% smoke free environment."
In the first 18 months after the town of Pueblo, Colorado enacted a smoking ban in 2003, hospital admissions for heart attacks dropped 27%. Admissions in neighboring towns without smoking bans showed no change, and the decline in heart attacks in Pueblo was attributed to the smoking ban.
Recent surveys taken by the Society for Research on Nicotine and Tobacco demonstrates supportive attitudes of the public, towards smoke-free policies in outdoor areas. A vast majority of the public supports restricting smoking in various outdoor settings. The respondents reasons for supporting the polices were for varying reasons such as, litter control, establishing positive smoke-free role models for youth, reducing youth opportunities to smoke, and avoiding exposure to secondhand smoke.
Alternatives to smoking bans have also been proposed as a means of harm reduction, particularly in bars and restaurants. For example, critics of bans cite studies suggesting ventilation as a means of reducing tobacco smoke pollutants and improving air quality. Ventilation has also been heavily promoted by the tobacco industry as an alternative to outright bans, via a network of ostensibly independent experts with often undisclosed ties to the industry. However, not all critics have connections to the industry.
Multiple studies have been conducted to determine the carcinogenicity of environmental tobacco smoke to animals. These studies typically fall under the categories of simulated environmental tobacco smoke, administering condensates of sidestream smoke, or observational studies of cancer among pets.
Secondhand smoke is popularly recognized as a risk factor for cancer in pets. A study conducted by the Tufts University School of Veterinary Medicine and the University of Massachusetts linked the occurrence of feline oral cancer to exposure to environmental tobacco smoke through an overexpression of the p53 gene. Another study conducted at the same universities concluded that cats living with a smoker were more likely to get feline lymphoma; the risk increased with the duration of exposure to secondhand smoke and the number of smokers in the household. A study by Colorado State University researchers, looking at cases of canine lung cancer, was generally inconclusive, though the authors reported a weak relation for lung cancer in dogs exposed to environmental tobacco smoke. The number of smokers within the home, the number of packs smoked in the home per day, and the amount of time that the dog spent within the home had no effect on the dog's risk for lung cancer.
Animals like dogs, cats, squirrels, and other small animals are affected by not only second-hand smoke inhalation, but also nicotine poisoning. Domestic pets, especially dogs, usually fall ill when owners leave nicotine products like cigarette butts, chewing tobacco, or nicotine gum within reach of the animal. Littered cigarette butts from smokers are a problem for small animals that mistake them for food if they find them on sidewalks or trashcans. Cigarette butts are the remains of a cigarette after smoking which contain the filter which is meant to contain tar, particles, and toxins from the cigarette such as ammonia, arsenic, benzene, turpentine and other toxins.
