image for second hand smoke Secondhand tobacco smoke contains over 4,700 chemical compounds. More than 200 of these are known poisons, such as carbon monoxide, hydrogen cyanide, and methyl isocyanate. There are also over 60 potentially carcinogenic substances, including nitrosamines, aromatic amines, benzene, benzopyprene, and formaldehyde.

In addition to these toxins, nonsmokers who are exposed to environmental tobacco smoke (ETS) absorb nicotine, the physically addictive component of tobacco. Once absorbed by the body, nicotine is broken down into cotinine. Scientists can use a highly specific blood test for cotinine to determine the amount of ETS exposure. After conducting many tests like these, researchers say there is strong and convincing evidence that secondhand smoke poses serious health risks.

This scientific opinion was again confirmed in 2006 by the release of an important document entitled “The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General." In this report, Dr. Carmona spelled out six important conclusions about secondhand smoke:

  • Exposure is widespread.
  • Exposure is associated with disease and premature death.
  • Exposed children are at particular risk of respiratory disorders and sudden infant death syndrome (SIDS).
  • Adults may suffer immediate harm from exposure, and both heart disease and cancer are caused by second hand smoke.
  • There is no risk-free level of exposure.
  • Only prohibiting of indoor smoking is effective in reducing exposure and risk.


Although one well-publicized 2003 study did not find a link between cancer and secondhand smoke, results from over 50 trials in the last 25 years have convinced most researchers that ETS can lead to lung cancer . For nonsmoking spouses of smokers, passive smoking increases the risk of lung cancer by 20% for women and 30% for men.

In 2002, the International Agency for Research on Cancer (an affiliate of the World Health Organization) concluded that “there is sufficient evidence that involuntary smoking (exposure to secondhand or ‘environmental’ tobacco smoke) causes lung cancer in humans.”

In the US, secondhand smoke causes an estimated 3,000 lung cancer deaths per year, according to the Environmental Protection Agency. (By comparison, active cigarette smoking leads to over 161,840 lung cancer deaths yearly.) The Agency classifies ETS as a Group A carcinogen—a category reserved only for the most dangerous cancer-causing agents in humans.

In addition to lung cancer, scientists have linked ETS to nasal sinus cancer and are studying possible associations with the following types of cancer:

There is some evidence that pets that live in smoking households have a higher risk of certain cancers. Secondhand smoke may be as dangerous to other animals as it is to humans.

Heart Disease

According to the American Heart Association, there are 135,000 deaths each year due to smoking-related cardiovascular disease. A landmark study reported that people exposed to ETS have double the risk of having a heart attack .

The nicotine in tobacco increases heart rate and blood pressure . The other toxins in cigarette smoke also promote blood clotting and damage the inner lining of the arteries, including the arteries of the heart. Exposure to ETS also impairs coronary artery circulation in healthy nonsmokers, according to a study published in the Journal of the American Medical Association . Within 30 minutes after exposure to ETS, the coronary arteries of nonsmokers function as poorly as those of regular smokers. Research indicates the abnormal changes—when repeated—encourage plaque buildup in coronary arteries that can lead to heart disease.

All in all, the risk of death due to heart disease is increased by about 30% among those exposed to ETS, an editorial accompanying the article notes. This compares with a doubling or quadrupling of risk associated with active smoking. “Thus, the effect of passive smoking is as high as one third the effect of active smoking,” the editorial says.

Asthma in Adults

Secondhand smoke at the workplace and at home is significantly associated with the development of asthma in adults. Many adults report that they have the most exposure to and symptoms from secondhand smoke during travel. While restaurants can be sources of exposure to ETS, some researchers have described “5 Bs” which pose the highest risk: bars, bowling alleys, billiard halls, bingo parlors, and betting establishments. On a positive note, some cities, towns, and states in the US have passed laws against smoking in bars and restaurants.

Illnesses In Children

While the risk of death from ETS is highest in older adults, children are especially susceptible to the harmful effects of ETS. Children who unknowingly breathe smoke are more likely to develop ear infections, respiratory symptoms (eg, phlegm, couging), asthma, and other respiratory diseases. Children who have asthma and are exposed to secondhand smoke may also suffer from sleep problems.

ETS causes up to 300,000 lower respiratory infections—such as pneumonia and bronchitis —each year in US children less than 18 months of age, resulting in as many as 15,000 hospitalizations. ETS is also associated with sudden infant death syndrome .

Human Reproduction

Less is known for certain about reproductive risks associated with second hand smoke. It is well established that active smoking is associated with both male and female infertility . It is also a major cause of low birth weight in infants. Some evidence suggests that second hand smoke may also impair fertility and lead to smaller babies. Further studies will be needed to assess these concerns.

Is There a Safe Limit?

At any age, ETS can cause irritation of the eyes, nose, throat, and lungs, as well as coughing and chest discomfort. It also kills up to 53,000 nonsmokers each year from respiratory illnesses, heart disease, or cancer—making it the third leading preventable cause of death in the US. A large body of data indicates these detrimental effects occur even at very low levels of exposure.

There are no safe levels of secondhand smoke, says the American Cancer Society, which recommends reducing exposure to the lowest possible amount. Studies suggest that separate nonsmoking areas in restaurants and other establishments may not adequately reduce exposure among patrons. For your health and that of your family, go to smoke-free establishments, avoid smoke-filled “5 B’s”, and eliminate secondhand smoke at home.