But it's a risk that can be mitigated. And Health Canada wants homeowners to measure the radon in their dwellings and take steps to lower levels if they are high.
"It can be fixed. It's easy to fix. And while it's not cheap, it's not super expensive either," Kelley Bush, head of radon education and awareness at Health Canada, said Thursday in an interview.
Radon is the second leading cause of lung cancer after smoking, responsible for about 16 per cent of lung cancer cases among Canadians. Lung cancer is the Number 1 cancer killer in Canada for both men and women.
But few people are aware of radon and few know of its link to lung cancer.
A survey released Thursday by Lung Cancer Canada underscores that problem. It showed that only one per cent of Canadians are aware of the fact that radon exposure is the second leading cause of lung cancer.
"I get calls from people who have lung cancer who've never smoked a day in their life and just found out that their home has high levels," Bush said. "And they're scared not only for themselves, but for their other family members who have been living in that house."
All houses have some radon; it's a byproduct of uranium. As the mineral breaks down in soil, it releases radon. The gas works its way into buildings through cracks in foundations or gaps around pipes.
A survey Health Canada released earlier this year showed that about seven per cent of homes in Canada have radon levels that top 200 becquerels per cubic metre. (A becquerel is the international unit for measuring radioactivity.) That is the threshold beyond which Health Canada says homeowners should take action.
Bush said the level of radon that is in a home depends on a number of factors, including the amount of uranium in the soil under and around the home, the type of soil on which the home sits and the type of ventilation system the house uses.
Levels also vary geographically. The Health Canada survey found under seven per cent of homes in Ontario had high levels of radon. But in New Brunswick, one in five homes topped 200 becquerels per cubic metre.
"If we could say it was one thing, in one place it would be a lot easier for Health Canada to get people to actually do something about it," Bush said.
"The only thing we can say is everyone should test, because it's really the only way to know."
Commercial tests are available through hardware stores. Health Canada recommends testing for a minimum of three months, starting in the fall when windows and doors in homes are typically closed. Tests are mailed away to a laboratory, which will return a reading.
While there are no safe levels of radon, Bush said, the 200 becquerels per cubic metre threshold was set after calculating potential health risks and the feasibility of asking people to make the changes needed to lower levels in a home.
Radon reduction efforts cost roughly between $1,500 and $3,000, she said. People interested in reducing the radon in their home should look for a contractor who is certified through the Canadian National Radon Proficiency Program.
"There's a standard method for radon reduction," Bush said. "While it's not inexpensive, it's a lot less expensive than windows or a new roof and it helps address a pretty serious health risk."
On the web:
Health Canada's radon survey, http://hc-sc.gc.ca/ewh-semt/radiation/radon/survey-sondage-eng.php
Health Canada's advice on how to lower a home's radon levels: http://www.hc-sc.gc.ca/ewh-semt/radiation/radon/protect-proteger-eng.php
Note to readers: This is a corrected story. An earlier version said the survey cited was commissioned by the Canadian Lung Association. In fact, it was commissioned by Lung Cancer Canada.