Q&A: Passive smoking
Tobacco smoke contains many chemicals
Pressure is mounting for a total ban on smoking in public places.
An update to a major review by the Government-appointed Scientific Committee on Tobacco and Health (SCOTH) has highlighted the health risks associated with passive smoking.
The British Medical Association is among those who believe a ban would make a signficant contribution to public health.
However, opponents say it would be draconian and unnecesary.
Online examines the evidence.
What is passive smoking?
Simply, breathing in other people's tobacco smoke. This is made up of "sidestream" smoke from the burning tip of the cigarette, and "mainstream" smoke that has been inhaled and then exhaled by the smoker.
Sidestream smoke accounts for nearly 85% of the smoke in a room.
What's in the smoke?
Tobacco smoke contains over 4000 chemicals in the form of particles and gases.
The particulate phase includes tar, nicotine, benzene and benzo(a)pyrene.
The gas phase includes carbon monoxide, ammonia, dimethylnitrosamine, formaldehyde, hydrogen cyanide and acrolein.
It has been estimated that tobacco smoke contains as many as 60 substances which cause - or are suspected of causing - cancer.
And many irritate the tissues of the respiratory system.
The Environmental Protection Agency (EPA) in the USA has classified environmental tobacco smoke as a class A carcinogen - ranking it alongside asbestos and arsenic.
What effect does it have on the passive smoker?
Breathing in other people's smoke can cause eye irritation, headache, cough, sore throat, dizziness and nausea. Just 30 minutes exposure can be enough to reduce blood flow through the heart.
There is also evidence to show that people with asthma can experience a significant decline in lung function when exposed.
Whether or not passive smoking can trigger new cases of asthma is a hotly debated issue.
What about in the longer term?
Non-smokers who are exposed to passive smoking in the home, have a 25% increased risk of heart disease and lung cancer.
Researchers from London's St George's Medical School and the Royal Free hospital have recently found when you include exposure to passive smoking in the workplace and public places the risk of coronary heart disease is increased by 50-60%.
A major review in 1998 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.
There is also some evidence to suggest that passive smoking may affect children's mental development.
SCOTH has looked at the data since 1998 and concluded secondhand smoke is damaging.
However, it is true that the health risks of breathing in other people's tobacco smoke are much smaller than those posed by actually smoking.
And the pro-smoking lobby, including the campaigning group FOREST, argue that the case against passive smoking has never been properly proved.
They point to a study by the University of California published in the British Medical Journal which found that the link between environmental tobacco smoke and coronary heart disease and lung cancer may be considerably weaker than generally believed.
This in turn, is disputed by the anti-smoking lobby, which points out that after considering the BMJ study, the UK Government's Committee on Carcinogens and SCOTH still concluded that environmental tobacco smoke is carcinogenic, and responsible for several hundred deaths a year in the UK.
How widespread is passive smoking?
Of course, anybody who regularly frequents pubs or bars is inevitably going to breathe in a significant amount of tobacco smoke.
However, a survey by the anti-smoking charity ASH in 1999 found that about 3million people in the UK are exposed to passive smoke at work.
And it is also estimated that almost half of all children in the UK are exposed to tobacco smoke at home.
One study found that in households where both parents smoke, young children have a 72% increased risk of respiratory illnesses.
Research also shows that children whose parents smoke in the home 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.
What do other countries do?
Banning smoking in public places is a highly controversial move, which has been resisted by the UK government so far.
However, some countries, including Ireland, Turkey and Norway, have accepted that a ban is the only way to tackle the problem of smoking effectively.
Despite concerns from the hospitality industry, the ban on smoking in public places in Ireland, which began in March this year, has not affected business, according to reports.