"Radon is a radioactive gas that you cannot see, smell or taste and can get into your home undetected. It is the second leading cause of lung cancer after smoking and the leading cause of lung cancer for non-smokers. When radon escapes from the ground into the outdoor air it is diluted to low concentrations and is no cause for concern. However, when radon enters an enclosed space, like a home, it can accumulate to high levels and become a health hazard..."
Health Canada