City health officials are encouraging residents to test their homes for harmful levels of radon this month.

The Chicago Department of Public Health is participating in National Radon Action Month by encouraging all residents to test their homes, according to a statement from the department.

“Radon kills more than 20,000 Americans each year,” Dr. Julie Morita, acting commissioner of public health, said in the statement.  “Many of these deaths are preventable thanks to low-cost home testing.  We call on residents to test their homes in order to help protect themselves and their families.”

Radon is a colorless, odorless radioactive gas that occurs naturally in nearly all soils and can seep into homes through cracks in foundations, health officials said. It is the leading cause of lung cancer among non-smokers.

The health department said cold winter months when windows are shut are the best time to test for elevated levels of radon.

Do-it-yourself radon test kits are available online and at home improvement or hardware stores, the department said. Information about testing is available on the EPA website or from the Cook County Radon Hot Line, (708) 865-6177.