Tobacco Active and Passive Smoking

6. Does passive smoking cause cancer?

• 6.1 Does passive smoking increase the risk of lung cancer?
• 6.2 What is known about passive smoking and other human cancers?
• 6.3 Does passive smoking cause cancer in animals?

6.1 Does passive smoking increase the risk of lung cancer?

Passive smoking involves exposure to the same numerous carcinogens and toxic substances which cause lung cancer in smokers. This implies some risk of lung cancer from exposure to secondhand smoke.

More than 50 studies have been published on lung cancer risk in people who have never smoked but who have been exposed to tobacco smoke, especially spouses of smokers. Most studies show an increased risk, particularly for persons with higher exposures. The overall finding is an increased risk of lung cancer in spouses of smokers of 20% in women and 30% in men. Non-smokers exposed at the workplace have a 12-19% increased risk of lung cancer.

This evidence is sufficient to conclude that passive smoking is a cause of lung cancer in never-smokers. More...

6.2 What is known about passive smoking and other human cancers?

The evidence of a possible link between breast cancers and passive smoking is inconsistent. Some studies have reported an increased risk, but this has not been confirmed by other large studies. Moreover, the lack of association between active smoking and breast cancer argues against a risk from passive smoking. Data are conflicting and sparse for cancers in other parts of the body.

Evidence for an association of childhood cancer and parental smoking is inconsistent and may be biased. A possible link between maternal smoking during pregnancy and childhood cancer has been suggested. Some studies also suggested that paternal smoking may be linked to a small increased risk for cancer of the lymphatic system, but results may have been biased. More...

6.3 Does passive smoking cause cancer in animals?

In laboratory experiments, animals are exposed to mixtures of smoke produced by machines to simulate secondhand smoking. Though such experiments do not fully simulate human exposure and the tumours induced are not completely representative of human cancer, results of animal studies help to understand the carcinogenic potential of secondhand tobacco smoke.

Lung tumours have been induced in mice when exposed to such tobacco smoke mixtures under different conditions.

Cigarette smoke condensates derived from sidestream and/or mainstream smoke produced skin tumours in mice when applied on the skin and lung tumours when injected into the lungs. An increased risk of cancer has been reported in dogs exposed to secondhand tobacco smoke in homes. More...