St. Louis, Missouri – A dangerous gas could already be building inside homes across eastern Missouri as cool spring nights keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk increases quickly when airflow is limited during overnight temperature swings common this time of year.
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, sump pumps, and crawl spaces. Missouri is considered a moderate- to high-risk state, with elevated radon levels frequently detected across St. Louis County and surrounding areas, where some homes exceed the EPA action level of 4 picocuries per liter.
In St. Louis and nearby communities including St. Charles, Florissant, and Chesterfield, homes with basements are especially vulnerable during early spring. Residents often keep homes sealed overnight to manage lingering cool air, which can trap radon indoors. The Missouri Department of Health and Senior Services warns that radon is the second leading cause of lung cancer in the United States, linked to about 21,000 deaths annually.
Radon exposure produces no immediate symptoms, making testing critical. Short-term test kits can return results within 48 to 96 hours, and mitigation systems can reduce indoor levels by up to 99 percent when properly installed.
Residents are urged to test homes now as conditions through April continue to support indoor buildup. Additional advisories may be issued as risks persist into early summer across the region.
