Short answer
Radon is the second leading cause of lung cancer in Canada after smoking and the leading cause in people who have never smoked. It’s linked to about 16% of Canadian lung cancer deaths, more than 3,000 a year, and roughly 850 a year in Ontario. Risk depends on the concentration and the number of years you breathe it, and it is much higher for smokers.
Key facts
- More than 3,000 lung cancer deaths a year in Canada are attributed to radon (about 16%).
- In Ontario, roughly 850 lung cancer deaths a year are attributed to radon.
- Lung cancer risk rises about 16% for every 100 Bq/m³ of long-term exposure.
- Radon is not linked to short-term symptoms. The harm is cumulative.
How radon damages the lungs
When you breathe in air containing radon, most of the radon gas is breathed back out. The problem is its decay products. These short-lived radioactive particles attach to dust and droplets, lodge in the lining of your airways, and release alpha radiation as they decay. Alpha particles don’t travel far, but at close range they can damage the DNA of lung cells. Over years, that damage can lead to cancer.
Radon doesn’t cause headaches, coughing or other short-term symptoms. You won’t feel it. That’s why it’s easy to ignore, and why testing matters.
How big is the risk?
A 2023 analysis in the Canadian Medical Association Journal attributed about 16% of lung cancer deaths in Canada to radon, more than 3,000 deaths a year. In Ontario, researchers estimated radon accounts for about 13.6% of lung cancer deaths, around 850 a year: more than two people every day.
The same Ontario study made a point that surprises many people: because so many homes have moderate radon, most radon-attributable cancers come from homes below the 200 Bq/m³ guideline. Getting high homes down matters most for each family living in one, but lower is better for everyone.
Smoking multiplies the risk
Radon and tobacco smoke work together. For people who smoke, the extra lung cancer risk from a given level of radon is many times higher than for people who have never smoked. In the CMAJ’s estimate, someone exposed to 200 Bq/m³ over a lifetime faces a lung cancer risk of roughly 17% if they smoke, compared with about 2% if they have never smoked. About 84% of Ontario’s radon-related lung cancer deaths were estimated to occur in people who had ever smoked.
That doesn’t make radon a smokers-only problem. For people who have never smoked, radon is the number one cause of lung cancer.
Level × time: why long-term exposure is what counts
Risk depends on two things: the concentration you breathe and how many years you breathe it. That’s why Health Canada’s guideline is based on a yearly average, and why the rooms that matter most are the ones where you spend the most time. A basement bedroom at 300 Bq/m³ contributes far more exposure than a storage room at the same level.
- Children have more years of potential exposure ahead of them, which is one reason to test while they’re young. Risk by age, and a checklist for before a baby comes home.
- People who work from home in a basement office or spend most of the day at home accumulate more exposure.
- Former smokers remain at higher risk and benefit from lowering radon.
Why the damage can’t be undone
Alpha radiation can leave changes in the DNA of airway cells. Cells repair most of the damage, but errors that are copied as cells divide stay in that cell line, and nothing reverses them. Lowering radon stops new damage and lowers future risk; it can’t repair what has already happened, which is one more reason to test early. How radon damage works.
The good news
Radon exposure is one of the most controllable cancer risks there is. A long-term test costs little. If your level is high, a mitigation system typically cuts it by 90% or more, permanently, for the cost of a minor renovation. Stopping smoking and lowering radon together reduce risk the most.
Common questions
Can radon cause cancers other than lung cancer?
Lung cancer is the established health risk from residential radon. Research into other cancers has not shown a clear link at household levels.
How long does it take for radon to cause lung cancer?
Radon risk builds over years to decades of exposure. There are no short-term symptoms, and lowering your exposure at any age reduces future risk.
Should I see a doctor if my radon is high?
There is no medical test for radon exposure. If you are worried, especially if you smoke or used to smoke, talk to your doctor about lung health and screening eligibility. The practical step is to lower the radon.
Sources
- CMAJ (2023) — Radon is responsible for 16% of lung cancer deaths in Canada
- Peterson et al., Cancer Causes & Control (2013) — Lung cancer risk from radon in Ontario
- Public Health Ontario — Radon infographic
- Health Canada — Radon: what you need to know
- World Health Organization — WHO Handbook on Indoor Radon (2009)