San Francisco, CA – As winter weather brings cooler temperatures and increased rainfall to Northern California, health officials are warning residents—especially those in San Francisco and across the Bay Area—about a dangerous indoor health threat that often goes unnoticed. January marks National Radon Action Month, drawing attention to radon gas, commonly referred to as the “invisible killer” inside the home.
According to the U.S. Environmental Protection Agency (EPA), radon is a naturally occurring radioactive gas released from soil and rock. It can seep into homes through foundation cracks, basements, crawl spaces, and utility openings. While California is often viewed as a lower-risk state overall, officials say elevated radon levels have been detected in parts of Northern California, including the Bay Area, Sacramento Valley, and foothill regions.
Health experts say winter conditions can increase radon exposure. In San Francisco and surrounding Northern California communities, homes are often closed up during cooler, wetter months, allowing radon to accumulate indoors. Long-term exposure to radon is the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths each year. Smokers face the greatest risk, but non-smokers are also vulnerable.
Unlike carbon monoxide, radon exposure does not cause immediate symptoms. Medical professionals warn the damage often occurs silently over many years, making home testing the only reliable way to detect dangerous levels.
State and federal health officials recommend that Northern California residents test their homes—especially during winter when radon concentrations can be higher. Test kits are affordable and widely available, and mitigation systems can significantly reduce radon levels when elevated readings are found.
As National Radon Action Month continues, officials urge Californians to test now to help protect their families from a serious but preventable health risk.
