San Francisco, California – A dangerous gas could already be building inside homes along the Pacific Coast as cool spring nights and shifting marine air keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk can increase quickly overnight as coastal temperature swings and damp conditions limit ventilation.
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, crawl spaces, and slab floors. The Pacific Coast region—including California, Oregon, and Washington—is generally considered a lower to moderate radon-risk area, but elevated levels have been detected in pockets across all three states, particularly inland and in areas with varied geology.
Across major metros like Seattle, Portland, and San Francisco, homes with basements and crawl spaces remain vulnerable during seasonal transitions. Coastal moisture and cooler overnight air often lead residents to keep homes sealed, trapping radon indoors and allowing concentrations to build without detection.
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 along the Pacific Coast are urged to test homes now as conditions through April continue to support indoor buildup. Free and low-cost test kits are widely available, and mitigation systems can significantly reduce indoor levels before risks increase into early summer.
