WILTON — January marks National Radon Action Month and the state Department of Public Health is encouraging residents to test their homes for this invisible and odorless but harmful gas.

Radon is the leading environmental cause of cancer deaths. It is a naturally occurring, radioactive gas formed from the natural decay of uranium. It is found in rock, soil, and water.

Health officials estimate that radon is responsible for more than 21,100 lung cancer deaths each year in the United States. While radon in outdoor air poses a relatively low risk to human health, it can enter homes from the surrounding soil and become a health hazard inside buildings.

DPH’s Lead Poisoning Prevention and Radon Program recommends that all Connecticut homes be tested for radon. Testing is simple, inexpensive, and should be conducted in the winter months when windows and doors are closed.

Test kits may be purchased from hardware stores or the American Lung Association by calling 1-800-LUNGUSA or visiting lung.org.

The U.S. Environmental Protection Agency recommends that homes with radon levels at or above 4.0 pCi/L be fixed. Smokers exposed to radon have a much higher risk for developing lung cancer.

Radon levels can be reduced by hiring nationally certified radon mitigation professionals.

To learn more about radon and to obtain a list of radon mitigation contractors, visit the DPH Radon Program website at ct.gov/radon.