United States
                   Environmental Protection
                    EPA 402-F-94-005
                    June 1994
                   Setting  the  Record  Straight:
                   Secondhand  Smoke  is A
                   Preventable  Health   Risk

       In early 1993, EPA released a report
 (Respiratory Health Effects of Passive Smoking:
 Lung Cancer and Other Disorders; EPA/600/6-
 90/006 F) that evaluated the respiratory
 health effects from breathing secondhand
 smoke (also called environmental tobacco
 smoke).  In that report, EPA concluded that
 secondhand smoke causes lung cancer in
 adult nonsmokers and impairs the respiratory
 health of children. These findings are very
 similar to ones made previously by the
 National Academy of Sciences and the U.S.
 Surgeon General.

       The EPA report classified secondhand
 smoke as a Group A carcinogen, a designation
 which means that there is sufficient evidence
 that the substance causes cancer in humans.
, The Group A designation has been used by
 EPA for only 15 other pollutants, including
 asbestos, radon, and benzene. Only
 secondhand smoke has actually been shown
 in studies to cause cancer at typical
 environmental levels. EPA estimates that
 approximately 3,000 American nonsmokers
 die each year from lung cancer caused by
 secondhand smoke.

       Every year, an estimated 150,000 to
 300,000 children under 18 months of age get
 pneumonia or bronchitis from breathing
 secondhand tobacco smoke. Secondhand
 smoke is a risk factor for the development of
 asthma in children and worsens the condition
 of up to one million asthmatic children.

       EPA has clear authority to inform the
 public about indoor air pollution health risks
and what can be done to reduce those risks.
EPA has a particular responsibility to do
everything possible to warn of risks to the
health of children.

      A recent high profile advertising and
public relations campaign by the tobacco
industry may confuse the American public
about the risks of secondhand smoke. EPA
believes it's time to set the record straight
about an indisputable fact: secondhand
smoke is a real and preventable health risk.

      EPA absolutely stands by its scientific
and well documented report. The report was
the subject of an extensive open review both
by the public and by EPA's Science Advisory
Board (SAB), a panel of independent
scientific experts. Virtually every one of the
arguments about lung cancer advanced by the
tobacco industry and its consultants was
addressed by the SAB. The panel concurred
in the methodology and unanimously
endorsed the conclusions of the final report.

      The report has also been endorsed by
the U.S. Department of Health and Human
Services, the National Cancer Institute, the
Surgeon General, and many major health

Classification of Secondhand Smoke as a
Known Human (Group A) Carcinogen

      The finding that secondhand smoke
causes lung cancer in nonsmoking adults is
based on the total weight of the available
evidence and is not dependent on any single
analysis. This evidence includes several
important facts.
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                                                           contains at least 50% recycled fiber

      First, it is indisputable that smoking
tobacco causes lung cancer in humans, and
there is no evidence that there is a threshold
below which smoking will not cause cancer.

      Second, although secondhand smoke
is a dilute mixture of "mainstream" smoke
exhaled by smokers and "sidestream" smoke
from the burning end of a cigarette or other
tobacco product, it is chemically similar to the
smoke inhaled by smokers, and contains a
number of carcinogenic compounds.

       Third, there is considerable evidence
that large numbers of people who do not
smoke  are exposed to, absorb, and
metabolize significant amounts of
secondhand smoke.

       Fourth, there is supporting evidence
from laboratory studies of the ability of


                    secondhand smoke both to cause cancer in
                    animals and to damage DNA, which is
                    recognized by scientists as being an
                    instrumental mechanism in cancer

                          Finally, EPA conducted multiple
                    analyses on the then-available 30
                    epidemiology studies from eight different
                    countries which examined the association
                    between secondhand smoke and lung cancer
                    in women who never smoked themselves but
                    were exposed to their husband's smoke.
                    Since the epidemiology studies are the major
                    thrust of the tobacco industry arguments
                    against the EPA report, these studies are
                    examined in more detail below.
   Active Smoking
    Causes Lung
   Cancer With No
   Evidence of A
 Secondhand &
 "Active Smoke"
Both Contain the
   Same 40
Exposure in
30 Epidemiology
Studies of ETS
and Lung
from Animal
Studies and
Genetic Tests
                                              Analysis of

The Epidemiology Studies

       The most important aspect of the
review of the epidemiology studies is the
remarkable consistency of results across
studies that support a causal association
between secondhand smoke and lung cancer.

       In assessing the studies several
different ways, it becomes clear that the
extent of the consistency defies attribution to
chance. When looking only at the simple
measure of exposure of whether the husband
ever smoked, 24 of 30 studies reported an
increase in risk for nonsmoking women with
smoking husbands.  Since many of these
studies were small, the chance of declaring
these increases statistically significant was
small.  Still, nine of these were statistically
significant, and the probability that this many
of the studies would be statistically
significant merely by chance is less than 1 in
10 thousand.

       The simple overall comparison of risks
in ever vs. never exposed to spousal smoking
tends to hide true increases in risk in two
ways.  First, it categorizes many women as
never exposed who actually received
exposure from sources other than spousal
smoking. It also includes some women as
exposed who actually received little exposure
from their husband's smoking.  One way to
correct for this latter case is to look at the
women whose husbands smoked the most.
When one looks at the 17 studies that
examined cancer effects based on the level of
exposure of the subjects, every study found
an increased lung cancer risk among those
subjects who were most exposed. Nine were
statistically significant. The probability of 9
out of 17 studies showing statistically
significant results occurring by chance is less
than 1 in ten million.

       Probably the most important finding
for a causal relationship is one of increasing
response with increasing exposure, since such
associations cannot usually be explained by
other factors. Such exposure-response trends
were seen in aU 14 studies that examined the
relationship between level of exposure and
effect. In 10 of the studies the trends were
statistically significant. The probability of
this happening by chance is less than 1 in a

       It is unprecedented for such a
consistency of results to be seen in
epidemiology studies of cancer from
environmental levels of a pollutant. One
reason is that it is extremely difficult to detect
an effect when virtually everyone is exposed,
as is the case with secondhand smoke.
However, consistent increased risks for those
most exposed and consistent trends  of
increasing exposure showing an increasing
effect provide strong evidence that
secondhand smoke increases the risk of lung
cancer in nonsmokers.

: Analysis of Individual Studies

24 of 30
"Ever" vs.
Showtd an

17 of 17
Studies Which
by Exposure
Level Showed
an Increased
Risk at the
Exposure Level
t j
r9 Were

9 Were

14 of 14

r10 Were ^
Significant I
                                5 of 6
                                Showed an
                               4 of 6 Were
 1 In 10,000  1 In 10 million  1 In a billion   1 In 10,000
        Probability of Occurrence by Chance

How Big a Lung Cancer Risk for Adults?

       The evidence is clear and consistent:
secondhand smoke is a cause of lung cancer in
adults who don't smoke. EPA has never
claimed that minimal exposure to secondhand
smoke poses a huge individual cancer risk.
Even though the lung cancer risk from
secondhand smoke is relatively small
compared to the risk from direct smoking,
unlike a smoker who chooses to smoke, the
nonsmoker's risk is often involuntary. In
addition, exposure to secondhand smoke
varies tremendously among exposed
individuals. For those who must live or work

in close proximity to one or more smokers, the
risk would certainly be greater than for those
less exposed.

       EPA estimates that secondhand
smoke is responsible for about 3,000 lung
cancer deaths each year among nonsmokers in
the U.S.; of these, the estimate is 800 from
exposure to secondhand smoke at home and
2,200 from exposure in work or social

The Risks to Children are Widely

       The conclusion that secondhand
smoke causes respiratory effects in children is
widely shared and virtually undisputed.
Even the tobacco industry does not contest
these effects in its media and public relations

       EPA estimates that every year, ,
between 150,000 and 300,000 children under
1-1/2 years of age get bronchitis or
pneumonia from breathing secondhand
tobacco smoke, resulting in thousands of
hospitalizations. In children under 18 years
of age, secondhand smoke exposure also
results in more coughing and wheezing, a
small but significant decrease in lung function,
and an increase  in fluid in the middle ear.
Children with asthma have more frequent and
more severe asthma attacks because of
exposure to secondhand smoke, which is also
a risk factor for  the onset of asthma in
children who did not previously have

Other Risks

       Secondhand smoke contains strong
irritants and sensitizers and many adults, as
well as children, suffer irritation and other
acute effects whenever they are exposed to
secondhand smoke. In addition, there is
mounting evidence that exposure to
secondhand smoke can have an effect on the
cardiovascular system, although the EPA
report does not  address this issue.
Tobacco Industry Media Campaign

       The tobacco industry is raising
numerous issues which may distract the
public from the fact that secondhand smoke
poses a real and preventable health risk. The
tobacco industry neither acknowledges nor
disputes EPA's conclusions of respiratory
effects in children.  It focuses instead on
EPA's findings on lung cancer.

       The overall thrusts of the tobacco
industry's arguments are that EPA
manipulated the lung cancer data to come to
a predetermined conclusion. The industry
also argues that a nonsmoker's exposure to
secondhand smoke is so small as to be
insignificant. The argument on minimal
exposure is belied both by the acute irritation
and respiratory effects and the fallacy of the
"cigarette equivalents" approach discussed
below. Responses to the specific criticisms of
EPA's assessment of the lung cancer data

The 11 U.S. Lung Cancer Studies

       Critics of the EPA report argue that by
normal statistical standards, none of the 11
U.S. studies included in the EPA report
showed a statistically significant increase in
the simple overall risk measure, and that EPA
should therefore have been unable to conclude
that secondhand smoke causes lung cancer in
nonsmokers. These critics are misrepresenting
a small part of the total evidence on
secondhand smoke and lung cancer.

       The consistency of study results in the
highest exposure category and exposure-
response trends discussed above also apply
to  the U.S. studies.  For example, seven of the
11 U.S. studies had fewer than 45 cases,
making statistical comparisons difficult.
Nonetheless, eight of the 11 had increased
overall risks, and for the seven studies which
reported on risks by amount of exposure, the
highest exposure groups in all seven had
increased risks. While the 11 U.S. studies are
not, by themselves, conclusive, they do

 support the conclusion that secondhand
 smoke is causally associated with lung cancer.

 Studies Completed Since Release of the EPA

       Critics claim that had EPA not
 "excluded" the recent Brownson study, the
 Agency could not have concluded that
 secondhand smoke causes cancer. In fact,
 four new lung cancer epidemiology studies,
 including the Brownson study, have been
 published since the literature review cutoff
 date for the 1993 EPA report, and aU support
 EPA's conclusions.  Three of these are large
 U.S. studies funded, at least in part, by the
 National Cancer Institute. A 1992 study of
 Florida women by Stockwell et al. found a
 60% overall increased risk of lung cancer from
 exposure to their husband's smoke, with
 significant results for both the highest
 exposure group and the exposure-response
 trend. The 1992 study of Missouri women by
 Brownson et al. found no overall increased
 risk, but did demonstrate a significant
 increase in risk in the highest spousal smoking
 exposure group and a positive exposure-
 response trend.

       The 1994 study by Fontham et al. of
 women in two California and three Southern
 cities is the largest case-control study on the
 subject ever conducted and is considered by
 EPA to be the best designed study on
 secondhand smoke and lung cancer
 conducted to date. This study found
 significantly increased risks for overall
 exposure and in the highest exposure group
 and a strong positive exposure-response
 relationship. These findings were significant
 not only for exposure from spouses, but also
 for exposure in the workplace and in social

 90% vs 95% Confidence Intervals

      Critics of the EPA report have charged
 that EPA changed the confidence interval in
 order to come to a predetermined conclusion.
 However, the conclusion that secondhand
smoke is a known human carcinogen simply
 does not hinge on whether or not a 95% or
90% "confidence interval" was used.  A
confidence interval is used to display
 variability in relative risk estimates in the
 epidemiology studies. As discussed above,
 the Group A designation is based on the total
 weight of the available evidence.  The
 consistency of results that are seen in the
 numerous studies examined lead to a
 certainty of greater than 99.9% that
 secondhand smoke increases the risk of lung
 cancer in nonsmokers.

       Use of what is called in statistics a
 "one-tailed test of significance," which often
 corresponds to a 90% confidence interval, is a
 standard and appropriate statistical
 procedure in certain circumstances.  The
 "one-tailed test" is used when there is prior
 evidence that if there is an effect from a
 substance, it is highly likely to be an adverse
 rather than a protective effect, or vice versa.
 In the case of secondhand smoke, an
 extensive database exists for  direct smoking
 indicating that if chemically similar
 secondhand smoke also has a lung cancer
 effect, this effect is likely to be similarly
 adverse.  EPA used one-tailed significance
 tests for lung cancer in both external drafts of
 the risk assessment document as well as the
 final report. Ninety percent confidence
 intervals were also used in other EPA cancer
 risk assessments, including methylene
 chloride, coke oven emissions, radon, nickel,
 and dioxin.

       In the non-cancer respiratory effects
 portions of the report, "two-tailed tests" and
 95% confidence intervals were used, since
 there was less prior evidence  from smokers to
 suggest that secondhand smoke would cause
bronchitis, pneumonia, and ear infections in

 The Meta-analysis

       Meta-analysis was used for the lung
 cancer data as an objective method of
combining results from many studies and was
 specifically endorsed by the SAB for use with
 this database.  Some critics argue both that
 the meta-analysis was not an appropriate
technique, and that had EPA  included the
Brownson study (addressed above) in the
meta-analysis of overall spousal exposure,
 EPA could not possibly have classified

secondhand smoke as a known human
carcinogen. This just isn't true.

       The finding that secondhand smoke is
a known cause of lung cancer in humans is
based on all the evidence and is not
dependent on the meta-analysis of the simple
ever- vs. never- exposed comparisons, as the
critics suggest. If the meta-analysis were
removed from the report entirely, the findings
would be precisely the same. The meta-
analysis was used primarily for estimating
and quantifying the population risks from
exposure to secondhand smoke, and an
alternative approach also used in the report
gave very similar results.


       In the secondhand smoke report, a
confounder would be a specific factor that
could be responsible for the lung cancer
increases observed in nonsmokers instead of
secondhand smoke.  The tobacco industry
and its consultants have suggested, for
example, that nonsmoking wives might share
in the same poor dietary habits as their
smoking husbands, increasing their risk.

       The consistency of results across
different countries where lifestyle factors,
including diet, vary,  argues against
confounding. For example, while the tobacco
industry theorizes that a high fat diet is a
confounding factor, the studies from Japan,
where dietary fat intake is among the lowest
in the world, show a strong dose-response
relationship for secondhand smoke and lung

       The EPA report did examine the
available data  for six potential confounders
such as occupation,  dietary factors, and
history of lung disease, and concluded that
none was likely to explain the lung cancer
increases seen  in the studies.

       The 1994 Fontham et al. study
controlled for diet and other potential
confounders, and concluded, "These
observations indicate that the strong
association in this study between adult
secondhand smoke exposure and lung cancer
risk cannot be attributed to any likely

The "Threshold Theory"

       Although some have argued that
tobacco smoke cannot cause cancer below a
certain level, there is no evidence that this
threshold exists.  In the absence of such
evidence, carcinogens at any level are
considered by EPA to increase risk
somewhat, although the degree of risk
certainly is reduced as exposure decreases.
The increased risks observed in the
secondhand smoke epidemiology studies are
further evidence that any threshold for
secondhand smoke would have to be at very
low levels.

"Cigarette Equivalents"

       The tobacco industry uses the
"cigarette equivalent" method of comparing
smokers' and nonsmokers' exposures to a
single component of tobacco smoke to infer
that a nonsmoker's exposure to tobacco
smoke is insignificant. However, the cigarette
equivalent method has no scientific support,
and was rejected by the SAB panel that
reviewed the EPA report.  Among the many
problems with this method is the fact that
while secondhand smoke and mainstream
smoke contain the same approximately 4,000
compounds, their ratios of individual
compounds differ by factors in the
thousands. Thus, there is no single compound
in tobacco smoke that is an adequate
indicator for drawing such comparisons. An
RJ Reynolds newspaper ad, while utilizing the
method, acknowledges it may not be relevant
for assessing risk from secondhand smoke.

 Residential Exposures Translated to the

       The tobacco industry frequently argues
that because most studies were based on
residential exposures, secondhand smoke has
not been shown to be a hazard in the
workplace. A substance capable of causing
cancer in one environment is certainly capable
of causing it in any other environment where
exposures are comparable, as is the case with

residential and workplace exposure to
secondhand smoke.  In fact, the 1994
Fontham study found a slightly higher risk for
workplace exposure than for residential

The Congressional Research Service (CRS) Report

       The RJ Reynolds' media campaign
cites a report prepared by the Congressional
Research Service (CRS) on cigarette taxes to
fund health care reform to argue that CRS
believes that the epidemiological evidence on
secondhand smoke and health effects is
"weak and uncertain." However, CRS has
not taken a position on either EPA's risk
assessment or the health effects of passive

       Two economists from CRS, citing
material largely prepared by the tobacco
industry, included a discussion of EPA's risk
assessment in an economic analysis of a
cigarette excise tax proposal to fund health
care reform. In EPA's view, the CRS
economists' cursory look at the issues is not
comparable to the exhaustive analyses and
rigorous review process which EPA undertook
when examining the extensive database on
secondhand smoke and respiratory health.
EPA is confident that a comprehensive
analysis of the secondhand smoke database
by expert scientists from CRS, with adequate
peer review, will come to conclusions about
the risks of secondhand smoke similar to
those of EPA and many other organizations.

Cigarette Prohibition

       The claim that the government is
attempting to bring back prohibition — this
time for cigarettes — is a complete fabrication
and utter nonsense.   EPA's interest is to
provide information to protect the nonsmoker
from involuntary exposure to a hazardous
substance.  Having a choice to take a risk for
themselves should not permit smokers to
impose a risk on others.
Secondhand Smoke Legislation

       Congress has recently passed, and
President Clinton has signed into law,
legislation restricting smoking in nearly all
public places where federal assistance is
provided for services to children.  Children
exposed to secondhand smoke almost never
have a choice. Protecting children from the
health effects of secondhand smoke should be
a priority for everyone.

       The Clinton Administration supports
pending legislation (H.R. 3434, S.1680,
S. 262) that would protect nonsmokers,
including children, from secondhand smoke in
most public places. These bills would not
take away the smoker's freedom to choose to
smoke, nor would it bring government
regulation into the home.

       The bills would also make good
economic sense. EPA estimates that
smoking restrictions would result in saving $4
billion to $8 billion per year in
housekeeping and maintenance expenses.

       Perhaps most importantly, the bills
would prevent thousands of premature
deaths of nonsmokers per year and reduce the
incidence of respiratory illness  in children.

For Further Information

       For additional information on
secondhand smoke and other indoor air
pollutants, call EPA's Indoor Air Quality
Information Clearinghouse.


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