Secondhand smoke
Action on Smoking and Health - March 2005
Introduction
Breathing other people's smoke is called passive, involuntary or
secondhand smoking. The non-smoker breathes "sidestream" smoke from the burning
tip of the cigarette and "mainstream" smoke that has been inhaled and then
exhaled by the smoker. Secondhand smoke (SHS) is a major source of indoor air
pollution.
What's in the smoke?
Tobacco smoke contains over 4000 chemicals in the form of particles and
gases. [1] Many potentially toxic gases are present in higher concentrations in
sidestream smoke than in mainstream smoke and nearly 85% of the smoke in a room
results from sidestream smoke. [2] The particulate phase includes tar (itself
composed of many chemicals), nicotine, benzene and benzo(a)pyrene. The gas
phase includes carbon monoxide, ammonia, dimethylnitrosamine, formaldehyde,
hydrogen cyanide and acrolein. Some of these have marked irritant properties
and some 60 are known or suspected carcinogens (cancer causing substances). The
Environmental Protection Agency (EPA) in the USA has classified environmental
tobacco smoke as a class A (known human) carcinogen along with asbestos,
arsenic, benzene and radon gas. 1
How does this affect the passive smoker?
Some of the immediate effects of passive smoking include eye irritation,
headache, cough, sore throat, dizziness and nausea. Adults with asthma can
experience a significant decline in lung function when exposed, while new cases
of asthma may be induced in children whose parents smoke. Short term exposure
to tobacco smoke also has a measurable effect on the heart in non-smokers.
Just 30 minutes exposure is enough to reduce coronary blood flow. [3]
In the longer term, passive smokers suffer an increased risk of a range
of smoking-related diseases. Non-smokers who are exposed to passive smoking in
the home, have a 25 per cent increased risk of heart disease and lung cancer.
[4] A major review by the Government-appointed Scientific Committee on Tobacco
and Health (SCOTH) concluded that passive smoking is a cause of lung cancer and
ischaemic heart disease in adult non-smokers, and a cause of respiratory
disease, cot death, middle ear disease and asthmatic attacks in children. [5]
A more recent review of the evidence by SCOTH found that the conclusions of
its initial report still stand i.e. that there is a "causal effect of exposure
to secondhand smoke on the risks of lung cancer, ischaemic heart disease and a
strong link to adverse effects in children". [6] A review of the risks of
cancer from exposure to secondhand smoke by the International Agency for
Research on Cancer (IARC) noted that "the evidence is sufficient to conclude
that involuntary smoking is a cause of lung cancer in never smokers". [7] A
study published in the British Medical Journal suggests that previous studies
of the effects of passive smoking on the risk of heart disease may have been
under-estimated. The researchers found that blood cotinine levels among
non-smokers were associated with a 50-60% increased risk of heart disease. [8]
Deaths from secondhand smoke
Whilst the relative health risks from passive smoking are small in
comparison with those from active smoking, because the diseases are common, the
overall health impact is large. Professor Konrad Jamrozik, formerly of Imperial
College London, has estimated that domestic exposure to secondhand smoke in the
UK causes around 2,700 deaths in people aged 20-64 and a further 8,000 deaths a
year among people aged 65 years or older. Exposure to secondhand smoke at work
is estimated to cause the death of more than two employed persons per working
day across the UK as a whole (617 deaths a year), including 54 deaths a year in
the hospitality industry. This equates to about one-fifth of all deaths from
secondhand smoke in the general population and up to half of such deaths among
employees in the hospitality trades. [9]
Risk to young children
Almost half of all children in the UK are exposed to tobacco smoke at
home. [10] Passive smoking increases the risk of lower respiratory tract
infections such as bronchitis, pneumonia and bronchiolitis in children. One
study found that in households where both parents smoke, young children have a
72 per cent increased risk of respiratory illnesses. [11] Passive smoking
causes a reduction in lung function and increased severity in the symptoms of
asthma in children, and is a risk factor for new cases of asthma in children.
[12] [13] Passive smoking is also associated with middle ear infection in
children as well as possible cardiovascular impairment and behavioural
problems. [14]
Infants of parents who smoke are more likely to be admitted to hospital
for bronchitis and pneumonia in the first year of life. More than 17,000
children under the age of five are admitted to hospital every year because of
the effects of passive smoking. [15] Passive smoking during childhood
predisposes children to developing chronic obstructive airway disease and
cancer as adults. 15 Exposure to tobacco smoke may also impair olfactory
function in children. A Canadian study found that passive smoking reduced
children's ability to detect a wide variety of odours compared with children
raised in non-smoking households. [16] Passive smoking may also affect
children's mental development. A US study found deficits in reading and
reasoning skills among children even at low levels of smoke exposure. [17]
Exposure to passive smoking during pregnancy is an independent risk
factor for low birth weight. [18] A recent study has also shown that babies
exposed to their mother's tobacco smoke before they are born grow up with
reduced lung function [19] Parental smoking is also a risk factor for sudden
infant death syndrome (cot death). For more detailed information about the
health effects of passive smoking on children see the ASH briefing: Passive
Smoking: The impact on children
What protection is there for non-smokers?
In the public health White Paper published in November 2004, the
Government set out proposals to ban smoking in most workplaces and public
places. However, exemptions are proposed for pubs that do not serve food and
private clubs. For further information about the White Paper proposals see
Factsheet no 14 in this series: Smoking in workplaces and public places.
Reports and surveys
Public opinion surveys have shown widespread support for smoking
restrictions in public places and this has been growing steadily in recent
years. The 2002 government commissioned survey of smoking attitudes found that
86% of respondents (including 70% of smokers) agreed that smoking should be
restricted at work and a similar proportion favoured smoking restrictions in
restaurants. The survey also revealed that a majority of people supported
smoking restrictions in pubs. [20]
A national survey commissioned by SmokeFree London found that over half
of non-smoking employees (51%) are still exposed to tobacco smoke at work, with
almost a third (31%) being exposed every day or most days. [21] A MORI
survey commissioned by ASH found that 80% of respondents favoured a law to
require all enclosed workplaces to be smokefree.[22] The same survey revealed
that about 2.2 million people in the UK are exposed to passive smoking in their
places of work.
