The Pennsylvania Department of Environmental Protection is warning residents about dangerously high levels of radon.
Radon is a naturally occurring radioactive gas that may cause up to 21,000 lung cancer deaths a year nationally.
A spokesperson for the agency says he could not share which area is affected.
The agency says at least one home has a radon level 25 times higher than recommended. In a letter sent to one resident, the agency says Pennsylvania generally has "some of the highest radon values in the country."