Does passive smoking increase your risk of cancer?

Passive smoking increases the risk of lung cancer in non-smokers by approximately 24%. This has been established on the basis of dozens of studies and is considered a convincing causal relationship. In the workplace, where people are sometimes exposed to tobacco smoke for hours a day, that risk rises to as high as 38%. The longer and more intense the exposure, the greater the danger.

The effect is not limited to the lungs. Across all cancer types combined, the risk for regularly exposed non-smokers is about 16% higher than for people who are not exposed. Women appear to be more vulnerable than men. For breast cancer, a similar increase of around 24% has been found, but the evidence for a causal relationship there is still limited: larger analyses rate this as weak. It is an indication, not a proven cause.

For oral cavity cancer, the figures are more concerning. On average, the risk is about 51% higher in people who are exposed to passive smoking. Those who are regularly exposed for more than ten to fifteen years have a risk that is more than twice as high as in people without that exposure. This is based on a limited number of studies, however, so the certainty is smaller than with lung cancer.

The reason passive smoking is harmful is that the same toxic substances that make active smoking dangerous are also present in environmental smoke, albeit at lower concentrations. Active smoking causes up to 30% of all cancer deaths worldwide and is associated with at least fifteen different types of cancer. Passive smoking is therefore not harmless, even if the concentrations are lower.