Five million people die every year around the world from diseases caused by smoking. That's a death every seven seconds. Of all the stuff crammed into a smoke, the three biggest harmful components are nicotine, carbon monoxide and tar.

Nicotine

The damage to health may be caused by the tar and poisonous chemicals, but it's the nicotine in tobacco which smokers can grow to depend upon.

Nicotine is a powerful and fast-acting stimulant drug. In small doses, it speeds up heart rate and increases blood pressure. This makes smokers feel more alert when they light up, while the brain activates a 'reward' system which is thought to be responsible for the pleasurable, relaxing 'hit' they describe. But in the long term, nicotine can actually lead to anxiety and depresses the ability of the brain to experience pleasure. Ex-smokers and non-smokers feel less anxious and depressed than smokers.

The effect on an individual smoker depends on a number of different factors:

• Physical build and current state of health
• The length of time they have been smoking
• How frequently they smoke
• The number of puffs they take, and how deeply the smoke is inhaled

Tar

This is a mixture of chemicals including formaldehyde, arsenic and cyanide. Ciggie smoke condenses when it's inhaled. This is a bit like watching droplets form upon the ceiling above a boiling kettle. The end result with smoking, however, is a whole lot more black and sticky. In fact about 70% of the tar present in tobacco smoke gets dumped into the lungs. It contains many substances which have been linked with cancer, as well as irritants that cause the narrow airways inside the lungs to get inflamed and clogged with mucus. It's the tar in cigarettes that stains fingers and teeth a brownish yellow.

Carbon monoxide

This is a poisonous gas found in high concentration in cigarette smoke, not to mention the stuff which coughs out of car exhaust pipes. Once inside the lungs, the carbon atoms grab any passing haemoglobin (the oxygen forming substance found in the blood) and basically take a joy ride around the body.

Someone who smokes 20 a day can have a carbon monoxide level which is five-10 times that of a non-smoker. This deprives the body of oxygen, which makes the blood sticky and can cause problems with the growth, repair and exchange of healthy nutrients.

Carbon monoxide reduces fitness and concentration. In particular, any reduction in oxygen levels is a real hazard to unborn babies. Pregnant women who smoke run a serious risk of miscarrying or having babies with low birth rate.

Ultimately, carbon monoxide can mess up electrical activity in the heart and encourage fatty deposits to clog up artery walls, increasing the risk of coronary heart disease and circulation problems.

Other chemicals present in tobacco smoke:

• Formaldehyde: used for pickling things in jars
• Acetone: found in nail varnish and paint stripper
• Ammonia: used in fertiliser and increases the addictive power of nicotine
• Hydrogen sulphide: smells of rotten eggs
• Polonium: a radioactive component
• Arsenic: a killer poison
• Benzene: petrol fumes
• Butane: lighter fuel
• DDT: insecticide
• Radon: radioactive gas

Updated: 13/04/2010