The Hazards of Secondhand Smoke

Secondhand smoke, also called environmental tobacco smoke (ETS), is the combination of two forms of smoke from burning tobacco products: sidestream smoke and mainstream smoke. Sidestream smoke, which makes up about half of all secondhand smoke, comes from the burning end of a cigarette, cigar, or pipe. Mainstream smoke is exhaled by the smoker. Exposure to secondhand smoke is also called involuntary smoking or passive smoking.

Chemicals Present in Secondhand Smoke
Many factors affect what chemicals are present in secondhand smoke. These factors include the type of tobacco, the chemicals added to the tobacco, how the product is smoked, and the paper in which the tobacco is wrapped. More than 4,000 chemicals have been identified in mainstream tobacco smoke; however, the actual number may be more than 100,000. Of the chemicals identified in secondhand smoke, at least 60 are carcinogens (substances that cause cancer), such as formaldehyde. Six others are substances that interfere with normal cell development, such as nicotine and carbon monoxide.

Some of the compounds present in secondhand smoke become carcinogenic only after they are activated by specific enzymes (proteins that control chemical reactions) in the body. After these compounds are activated, they can then become part of a cell's DNA and may interfere with the normal growth of cells. In 1993, the US Environmental Protection Agency (EPA) determined that there is sufficient evidence that secondhand smoke causes cancer in humans and classified it as a Group A carcinogen. In 2000, the US Department of Health and Human Services (DHHS) formally listed secondhand smoke as a known human carcinogen in The U.S. National Toxicology Program's 10th Report on Carcinogens. The most recent report can be found on the Internet.

Scientists do not know what amount of exposure to secondhand smoke, if any, is safe. Because it is a complex mixture of chemicals, measuring secondhand smoke exposure is difficult and is usually determined by testing blood, saliva, or urine for the presence of nicotine, particles inhaled from indoor air, or cotinine (the primary product resulting from the breakdown of nicotine in the body). Nicotine, carbon monoxide, and other evidence of secondhand smoke exposure have been found in the body fluids of nonsmokers exposed to secondhand smoke. Nonsmokers who live with smokers in homes where smoking is allowed are at the greatest risk for suffering the negative health effects of secondhand smoke exposure.

Health Effects
Secondhand smoke exposure is a known risk factor for lung cancer. Approximately 3,000 lung cancer deaths occur each year among adult nonsmokers in the United States as a result of exposure to secondhand smoke. Secondhand smoke is also linked to nasal sinus cancer. Some research suggests an association between secondhand smoke and cancers of the cervix, breast, and bladder. However, more research is needed in order to confirm a link to these cancers.

Secondhand smoke is also associated with the following non-cancerous conditions:

• chronic coughing, phlegm, and wheezing
• chest discomfort
• lowered lung function
• severe lower respiratory tract infections, such as bronchitis or pneumonia, in children
• more severe asthma and increased chance of developing asthma in children
• eye and nose irritation
• severe and chronic heart disease
• middle ear infections in children
• sudden infant death syndrome (SIDS)
• low birth weight or small size at birth for babies of women exposed to secondhand smoke during pregnancy

Certain other non-cancerous health conditions may also be associated with secondhand smoke. However, more research is needed in order to confirm a link between these conditions and secondhand smoke. These conditions include spontaneous abortion (miscarriage); adverse effects on cognition and behavior in children; and worsening of cystic fibrosis, a disease that causes excessive mucus in the lungs.

Reducing Nonsmokers' Exposure
In January 2000, the Department of Health and Human Services (DHHS) launched Healthy People 2010, a comprehensive, nationwide health promotion and disease prevention agenda designed to help improve the health of all people in the United States during the first decade of the 21st century. Several objectives of this program relate to tobacco use and exposure to secondhand smoke, including the goal of reducing the proportion of nonsmokers exposed to secondhand smoke from 65% to 45% by 2010.

Studies have shown that separating smokers and nonsmokers within the same air space may reduce, but not eliminate, nonsmokers' exposure to secondhand smoke. Individuals can reduce their exposure to secondhand smoke by not allowing smoking in their home or car. Educational, clinical, and policy interventions have also been shown to reduce secondhand smoke exposure. Such policies include adoption of worksite restrictions, passage of clean indoor air laws, and enforcement of smoking restrictions in shared environments.

On the national level, several laws restricting smoking in public places have been passed. For instance, effective January 1, 2005, smoking is banned in all DHHS buildings. In other Federal office buildings, smoking is limited to designated areas. Smoking is also banned on all domestic airline flights and nearly all flights between the United States and foreign destinations. All interstate bus travel is smoke-free. Smoking is also prohibited or restricted to specially designated areas on trains traveling within the United States.

Many states and local governments have passed laws prohibiting smoking in public facilities such as schools, hospitals, airports, and bus terminals. Some states also require private employers to create policies that protect employees who do not smoke, and several local communities have enacted nonsmokers' rights laws, most of which are stricter than state laws.

Information provided by the Cancer Information Service of the National Cancer Institute.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.