What are the main chemical components of secondhand smoke?

Secondhand smoke is a mixture of smoke given off by the burning end of a cigarette or tobacco product (sidestream smoke) and the smoke exhaled by the smoker (mainstream smoke diluted by ambient air) [2]. This smoke contains thousands of chemicals, hundreds of which are considered toxic and about 70 of which are known to cause cancer [1].

There is no safe level of exposure to secondhand smoke; even brief exposure can cause serious health damage [1]. These chemicals directly affect the respiratory, cardiovascular, and circulatory systems, increasing the risk of chronic diseases in nonsmokers. Their effects are even more severe in infants due to their developing bodies [1].

Toxic and Carcinogenic Compounds

Commercial tobacco smoke contains more than 7,000 chemicals, hundreds of which are toxic and about 70 of which can cause cancer [1]. These chemicals are present in the smoke inhaled by smokers as well as in secondhand smoke [2]. Prominent chemicals and toxins include:

• Benzene: A known carcinogen [2].
• Tobacco-specific nitrosamines: Potent carcinogenic compounds [2].
• Benzo[a]pyrene: A carcinogen [2].
• 1,3-Butadiene: A dangerous gas [2].
• Cadmium: A toxic metal [2].
• Formaldehyde: An irritant and carcinogen [2].
• Acetaldehyde [2].

The quantity and quality of these chemicals vary based on factors such as the type of tobacco used, additives (e.g., menthol), the method of smoking the product, and the material used to wrap the tobacco [2].

Measuring Exposure to Secondhand Smoke

Exposure to secondhand smoke can be measured in several ways, including testing indoor air for respirable suspended particles (particles small enough to reach the lower human respiratory tract) or individual chemicals like nicotine or other potential harmful components of tobacco smoke [2]. Exposure can also be assessed by measuring the level of biomarkers such as cotinine (a byproduct of nicotine metabolism) in a nonsmoker's blood, saliva, or urine [2]. Nicotine, cotinine, and other chemicals present in secondhand smoke have been found in the body fluids of nonsmokers exposed to it [2].

Common Locations of Exposure

Exposure to secondhand smoke commonly occurs in homes, workplaces, and public places such as restaurants and bars [1]. Homes and workplaces are significant sources of exposure due to the long periods people spend in these environments [2]. Young children and infants are particularly vulnerable at home [2]. Secondhand smoke can drift even if no one is smoking in the home, moving through hallways, stairwells, and ventilation systems in multi-unit housing [1].

Protecting Yourself and Your Family

The only way to fully protect against secondhand smoke is to completely eliminate smoking in indoor areas [1]. Opening windows, using fans or ventilation systems, or restricting smoking to certain rooms or times does not eliminate exposure to secondhand smoke [2]. For more information on how to prevent it, you can visit Secondhand Smoke: Its Hidden Health Risks for Nonsmokers and Children and How to Prevent It (Arabic).

If you live with a smoker, the best step is to encourage them to quit. In public places, look for locations that enforce a comprehensive smoking ban [1]. You should be especially cautious when it comes to children, as they are more susceptible to the health risks caused by secondhand smoke [1].

Medical references

• About Secondhand Smoke
• Secondhand Smoke and Cancer