The combustion of tobacco produces a type of smoke that contains more than 4000 substances and chemicals, which are made up of particles and gases that can be inhaled and absorbed into the body.

Many of these chemicals are extremely dangerous, not only for the smoker but also for those people nearby.

The International Cancer Investigation Agency has identified over 50 carcinogenic substances in tobacco smoke. 11 of the substances are proven to cause cancer in humans, 7 probably cause cancer in humans and 49 of the substances cause cancer in animals but have not yet been proven to in humans.

Other substances found in environmental tobacco smoke are certainly poisonous and most definitely none are beneficial to a person's health.

The U.S. Environmental Protection Agency (EPA) has classified environmental tobacco smoke as a Group A carcinogen. This means that there is more than enough evidence to prove that tobacco smoke, whether it is inhaled by the smoker or the non-smoker, can cause cancer in humans.

Mainstream and sidestream smoke both contain a huge number of toxic, poisonous and carcinogenic substances.

Surprisingly, sidestream smoke (smoke that escapes the end of a burning cigarette) contains much higher concentrations of many of the chemical compounds.

What's more is that the particles that make up sidestream smoke are much smaller than those of mainstream smoke. This means that these smaller particles that float in the air, will be inhaled much deeper into the lungs and will be able to reach the furthest and deepest corners within a person's respiratory system and therefore causing much more damage.

For example, cadmium, a known lung cancer causing substance, is found in concentrations that are six times higher in the smoke that is inhaled by passive smokers as opposed to the smoke that is inhaled directly by the smoker through the cigarette.

Even so, although 85% of the smoke that is present in a smoke-filled room is made up of sidestream smoke, passive smokers still have a lesser risk of suffering the effects of the harmful substances contained in tobacco smoke.

Three of the main components of environmental tobacco smoke are:

Nicotine - an addictive drug as powerful as cocaine or heroin. It alters the brain as well as a person's behaviour and mood. It is also used in insecticides.
Tar - a cancer causing substance that damages the lungs.
Carbon monoxide - a gas that replaces some of the oxygen in the body that is needed for the lungs to function properly. Carbon monoxide is a poisonous gas, which is also found in car exhaust fumes.

Some of the carcinogenic substances found in tobacco smoke are:

Tar - used to tarmac roads.
Arsenic - very potent deadly poison.
Cadmium and nickel - used in batteries.
Vinyl chloride - used to make vinyl products. Short-term exposure causes dizziness, headaches and tiredness. Long-term exposure can lead to cancer and liver damage.
Creosote - a component of tar. If inhaled it can cause irritation of the respiratory tract.
Formaldehyde - a preservative substance used in forensic labs. It causes cancer in humans and in animals.
Polonium 210 - a radioactive substance that requires special handling techniques when studied in labs. It can cause cancer of the liver and bladder, stomach ulcers, leukaemia amongst other diseases.

Other irritant toxins that are found in cigarette smoke are:

Ammonia - a pungent colourless gas used in many cleaning products such as window or glass cleaner.
Acetone - the main component of nail varnish remover.
Acrolein - an extremely toxic substance used to manufacture acrylic acid. It is considered a possible human carcinogen and it irritates the lungs and is the cause of emphysema.
Hydrogen cyanide - deadly toxic poison used to kill rats. If breathed in in small doses, it can cause headaches, dizziness and weakness.
Carbon monoxide - a deadly gas if inhaled in enclosed spaces. Faulty and leaking gas heaters, boilers, stoves and tobacco smoke all produce this gas.
Toluene - used to manufacture paint, paint thinners, nail varnish and adhesives. Low - moderate levels can provoke tiredness, weakness, loss of appetite and memory loss.

Although it is smokers who are mainly at risk from suffering the side effects of smoking, in reality, anyone who is regularly exposed to tobacco smoke is at risk of developing any smoking related disease.

For non-smokers who choose not to smoke, whatever their reason, it is unfair that they are not protected from secondhand smoke and the threat of developing a potentially life threatening illness from somebody else's habit.

Many adults die as a direct result of smoking each year and in fact smoking is the biggest cause of preventable death in the worlds.

Although relatively few people die from passive smoking, even still, hundreds and possibly thousands of people a year die unnecessarily from inhaling the tobacco smoke of those people around them.

No one in the world would willingly inhale or ingest such a concoction of harmful gases, chemicals and substances into their body. However, on smoking a cigarette or from inhaling the smoke from someone else's cigarette, that's exactly what you are doing.