Each year diseases caused by smoking tobacco kill about 19,000 Australians. Of lifetime smokers, half will die from their addiction, with 50% of these deaths occurring by middle age.

Tobacco smoke contains more than 4,000 chemicals, at least 43 of which are known to cause cancers, including of the lung, throat, mouth, bladder and kidneys. Tobacco smoke also causes other diseases, such as stomach ulcers, emphysema, strokes and heart disease, possibly contributes to osteoporosis, and can lead to fertility problems for both men and women.

During pregnancy, nicotine and other poisons in cigarette smoke reach the baby through the mother's bloodstream and can contribute to miscarriage and complications with the pregnancy and the birth. Babies of smokers are more likely to have a low birthweight and to be born early or to die around the time of birth. Smoking during pregnancy and after the birth is considered a major risk factor for sudden infant death syndrome (SIDS or cot death). Children of smokers are also more likely to have asthma and lung problems.

Nicotine, the addictive drug in tobacco, stimulates the nervous system but also makes the smoker feel relaxed. Mixed with carbon monoxide, it temporarily increases heart rate and blood pressure, and narrows small blood vessels under the skin. It slows blood flow, reducing oxygen to the feet and hands, resulting in some smokers having limbs amputated.

Tar is made up of many chemicals, including gases and carcinogens (substances that cause cancer) that coat the lungs like soot in a chimney. Smoking low-tar cigarettes may be of some help, but smokers tend to take deeper puffs and hold the smoke in for longer.

Carbon monoxide reduces the supply of oxygen to the muscles, brain and body tissue, making the entire body - especially the heart - work harder. Gradually, airways swell up and allow less air into the lungs.

New smokers often feel dizzy and sick from tobacco smoke; if they continue to smoke, their bodies come to depend on nicotine and they can smoke more and more. There is no 'safe' level of tobacco smoking.