Obviously, with the amount of chemicals, toxins and harmful substances that are contained in tobacco smoke, there are going to be adverse effects on your health if you breathe it in, whether you are a smoker or not.

With passive smoking, non-smokers are forced to breathe in secondhand smoke, which is made up of the smoke that escapes the end of the burning cigarette and the smoke that is exhaled out of the smoker's lungs. Both of these types of smoke contain just as many toxins, chemicals and carcinogenic substances as the smoke from the cigarette that the smoker inhales. This means that anyone breathing in secondhand smoke is exposed to the harmful effects of these substances, as is the smoker himself (see section on what does tobacco smoke consist of).

In fact, when a person smokes a cigarette, they only inhale 15% of the tobacco smoke themselves, as the rest escapes into the air for anyone around to breathe in. Studies show that if a non-smoker spends over two hours in a smoky room, during that time, they will have inhaled the equivalent of 4 cigarettes.

Some of the chemicals that are found in secondhand smoke, which include a number of carcinogens, are benzene, benzopyrene, formaldehyde, ammonia and hydrogen cyanide. It has also been found that secondhand smoke contains twice as much nicotine and tar and five times the amount of carbon monoxide than the mainstream smoke that is inhaled by the smoker. This means that passive smokers could be more at risk than smokers if exposed for long periods of time.

Sidestream smoke, which is the smoke that drifts from the top of the burning cigarette, may often contain higher levels of some of these chemicals, due to the fact that this smoke is produced at a cooler temperature and therefore the tobacco does not combust fully.

When a person smokes a cigarette, the hot smoke in the room rises, as hot air does. However, tobacco smoke tends to cool rapidly, which immediately stops its ascent upwards. The smoke is denser than air, which therefore causes it to descend to a level where smokers and non-smokers can do nothing but breathe in this smoky cloud.

If you breathe in tobacco smoke, you are damaging your body and your health. For every 8 smokers that die from a smoke-related illness, 1 non-smoker also dies with them.

For those who are not exposed every day to hours of breathing in other's smoke, the risk to your health is somewhat less, although if you suffer from asthma, inhaling secondhand smoke that has wafted over from a smokers table in a restaurant, for example, could trigger an attack.

Incidentally, and more worryingly, 10 -20 minutes exposure to secondhand smoke can increase the heart rate, constrict blood vessels and increase blood pressure. It can also restrict the flow of oxygen to the heart. All of these symptoms are associated with heart disease or a stroke.

Pregnant women should definitely not smoke themselves but even breathing in other people's tobacco smoke can have severe repercussions on her unborn baby, its health and its weight. (see section on smoking and pregnancy)

Non-smokers who are married to a smoker or who work in an environment where smoking is permitted suffer up to 60% higher risks of developing cancer or heart disease. Likewise children who are subjected to passive smoking in the home will more than likely suffer breathing difficulties, coughs, ear infections, or pneumonia, amongst other illnesses, and therefore have to take more time off school. Passive smoking has also been linked to poor results at school and severe behaviour disorders (see section on smoking and pregnancy).

Passive smoking in the short term can irritate the eyes, nose and throat and result in a headache, cough, chest pain, dizziness or feelings of sickness.

For people with asthma, the effects of passive smoking are more severe, as their lung function can be negatively affected and they may occur serious respiratory problems and wheezing. Asthmatic children will obviously be more at risk from exposure to passive smoking as their lungs are still developing. The EPA has estimated that between 200,000 and 1,000,000 children have seen their condition deteriorate due to the exposure to tobacco smoke. For more information see section on passive smoking and children.

In the long-term, adult passive smokers are at risk of the following:

20% - 30% increased risk of developing lung cancer. Environmental tobacco smoke has been classified as a Class A carcinogen and may also cause cancer of the bladder, cervix, throat and breast cancer.
25% increased risk of heart disease. Conclusive evidence exists and proves that non-smokers who live with smokers have higher risks of coronary heart disease than those who live in a smoke-free home. A report from the US Surgeon General in 1999 stated that secondhand smoke has been linked to up to 62,000 deaths from ischemic heart disease per year.
A significantly higher risk of frequently suffering chronic respiratory disorders, as the tobacco smoke may irritate the tissues of the respiratory tract. In 1979 the US Surgeon General reported that as a result of breathing in secondhand smoke adults and children were found to experience several adverse respiratory symptoms.
Narrowing of the carotid arteries, which are responsible for carrying blood to the brain.
Suffering from blood clots, due to the fact that tobacco smoke makes the blood denser and more likely to clot.
HDL cholesterol, which is the good cholesterol that protects the blood, is reduced.
The development of atherosclerosis or hardening and narrowing of the arteries. This process can start after 30 minutes exposure to environmental tobacco smoke.
Suffering a stroke.
Developing nose and sinus cancer.
An increased risk of cardiovascular disease, as blood vessels are damaged thus preventing any form of exercise to take place and cholesterol levels to rise.