Phoenix, Arizona – A dangerous gas could already be building inside homes across central Arizona as warm spring days and cooler overnight temperatures keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk can increase quickly when airflow is limited, especially in tightly sealed homes using air conditioning.
According to the U.S. Environmental Protection Agency, radon is a radioactive gas that forms naturally in soil and can enter homes through foundation cracks, slab floors, and utility openings. Arizona is generally considered a low- to moderate-risk state, but elevated radon levels have been detected in Maricopa County and surrounding areas, with some homes exceeding the EPA action level of 4 picocuries per liter.
In Phoenix and nearby communities including Mesa, Chandler, and Glendale, homes built on slab foundations are especially vulnerable during seasonal transitions. Residents often keep homes sealed overnight to maintain indoor temperatures, which can trap radon indoors. The Arizona Department of Health 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 the only reliable way to detect it. 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.
