Lung cancer is usually caused by smoking – but not always. Researchers say that more than 90% of lung cancers in men and at least 70% in women are directly caused by cigarette smoking1.
Lung cancer can also be caused by other things. Some people who have lung cancer have never smoked a day in their lives. Their cancer may be caused by something else, like:
- Second-hand smoke. People who regularly breathe second-hand smoke have almost double the risk of getting lung cancer than people who stay away from smoke1. It's a fact: Non-smokers who live or work in smoky air can get lung cancer from second-hand smoke.
- Radon. Radon is a colourless, odourless gas found in the soil. Radon can enter buildings through cracks in the foundation or insulation, or through drains or walls. Radon can get trapped in basements and other places that don't have a lot of air flow (fresh air). People who have a high exposure to radon are at higher risk of lung cancer. Read more about radon, an invisible gas that can cause lung cancer
- Asbestos. Asbestos is a heat-resistant mineral found in some workplaces and homes. It has been used in brake pads, insulation, siding, and many other products. People who have a high exposure to asbestos are at higher risk of lung cancer. Read more about asbestos and how it can cause lung disease
- Other toxic products: uranium, arsenic, some petroleum products may also increase the risk of developing lung cancer
Percentage of lung cancer associated with smoking: "Probably more than 90% of lung cancers in men and at least 70% in women are directly attributable to cigarette smoking". Cancer Care Ontario, Cancer Incidence and Mortality in Ontario, 1964-2002