Minneapolis, Minnesota – A dangerous gas could already be building inside homes across the Upper Midwest as cool spring nights keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk can increase rapidly overnight as fluctuating temperatures lead residents to seal homes against lingering cold.
According to the U.S. Environmental Protection Agency, radon is a radioactive gas that forms naturally in soil and seeps into homes through foundation cracks, basements, and crawl spaces. The Upper Midwest—including Minnesota, Wisconsin, Iowa, North Dakota, and South Dakota—is among the highest radon-risk regions in the country, with some states reporting that over 40% of homes exceed the EPA action level of 4 picocuries per liter.
Across cities like Minneapolis, Milwaukee, Fargo, Sioux Falls, and Des Moines, homes with basements are especially vulnerable this time of year. The region’s glacial soils and widespread basement construction create ideal pathways for radon to enter and build indoors, particularly when homes are sealed overnight.
Health officials warn radon is the second leading cause of lung cancer in the United States, linked to about 21,000 deaths annually. The gas produces no smell or immediate symptoms, making testing the only reliable way to detect it.
Residents across the Upper Midwest are urged to test homes now as conditions through April continue to trap indoor air. Free and low-cost test kits are widely available, and mitigation systems can significantly reduce indoor levels before risks increase into early summer.
