Pennsylvania is urging residents of the Center Valley area of Lehigh County to have their homes tested for radon after recent test results showed extremely high levels of the gas.

Radon is an odorless, colorless, radioactive gas that comes from the natural breakdown of uranium in the rock and soil beneath houses.

The state Department of Environmental Protection says several homes in Center Valley were found to have radon levels hundreds of times higher than what federal regulators deem unsafe.

Radon tends to build up in homes during cold weather when folks keep their doors and windows shut, said spokeswoman Colleen Connolly.

"The radon comes up through the foundation of the home or through the cracks in the openings," she said. "The home is sealed, the doors and the windows, so there's no place for the radon to escape."

Radon is the second leading cause of lung cancer in the U.S. behind smoking, so the DEP is urging all Pennsylvanians to have their homes tested and those with radon systems to check they're working properly.

The DEP will hold a radon open house for Center Valley area residents on Dec. 4 from 4 to 8 p.m. at the Upper Saucon Township Municipal Building, 5500 Camp Meeting Road, Center Valley.

"Residents will get a list of the area companies that are certified by DEP to perform radon testing or do mitigation," Connolly said.