Leaders from the Pennsylvania Department of Environmental Protection Department of Health are encouraging Pennsylvanians to do a simple test for radon in their homes as part of National Radon Action Month.

Radon is an invisible, odorless radioactive gas that enters homes from the ground as a result of the breakdown of uranium and radium in rocks and soil.

Due to Pennsylvania’s terrain, some of the highest radon levels in the United States have been found in homes around the state, according to a news release from the DEP.

While a radon test can be done any time of year, winter is ideal because doors and windows are closed, providing more accurate results.

The DEP provides a list of radon service providers on its website.

“The danger in radon exposure is that you can’t see it, taste it, or smell it; and you won’t have any symptoms to alert you, but over time if you are breathing in high levels of radon, it can cause lung cancer,” Physician General Dr. Denise Johnson said. “I encourage you to get your home tested and fixed to improve your and your family’s health and safety.”