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What is secondhand smoke?

Over the past 30 years, a growing body of scientific evidence has concluded that secondhand smoke can harm the health of nonsmokers. As this became accepted by the public, smokers' arguments on their right to light up were overtaken by the rights of the nonsmoking majority to be protected from other people's tobacco smoke.

What is secondhand smoke?

The process of smoking produces three different types of tobacco smoke:

1. Mainstream smoke: This is smoke directly inhaled by the smoker through a burning cigarette.

2. Exhaled mainstream smoke: This is smoke breathed out by the smoker.

3. Sidestream smoke: This is smoke which drifts from the burning end of a cigarette.

Secondhand smoke (SHS) is the combination of exhaled mainstream smoke and sidestream smoke. Secondhand smoke is also called environmental tobacco smoke (ETS). Breathing in secondhand smoke is also referred to as passive smoking.

Secondhand smoke affects the health of both nonsmokers and smokers. There are at least 250 chemicals in secondhand smoke that are known to be toxic, including more than 50 that are known to cause cancer.

Sidestream smoke contains a range of chemicals similar to mainstream smoke. However, the amounts of certain chemicals found in sidestream smoke are different to mainstream smoke. In some cases their levels are more than ten times higher than in the smoke inhaled by the smoker. For example, compared to mainstream smoke, sidestream smoke contains greater amounts of ammonia, acrolein, carbon monoxide, nicotine and a number of cancer causing chemicals, per cigarette.

However, sidestream smoke is diluted by being mixed with air before being inhaled. People breathing in secondhand smoke receive lower levels of toxic chemicals than active smokers, who draw the tobacco smoke directly into their lungs. This means active smoking is more dangerous to health than breathing in secondhand smoke.

For more information see Secondhand smoke