Radon is present in all homes in some amount — even our atmosphere carries it, averaging 0.4 pCi/L. A home built over or near a significant radon source can trap that gas indoors at unsafe levels.
There is no "safe" level of radon. Any exposure carries some risk.
According to the EPA, radon causes about 21,000 lung cancer deaths in the U.S. every year, roughly 13 to 14% of all lung cancer deaths.
According to the EPA, living with radon at 4.0 pCi/L, about 7 out of every 1,000 non-smokers could get lung cancer, the same as the risk of dying in a car crash. For smokers it’s about 62 out of 1,000.
Radon is the #1 cause of lung cancer among non-smokers and the second leading cause overall, behind smoking.
Radon won't kill you overnight like carbon monoxide. The risk comes from long-term exposure — and your home is the primary source.
Radon is pulled into your home by "stack effect" — higher pressure in the colder soil versus lower pressure from warmer temperatures indoors, similar to the draft a wood stove creates. Radon levels are higher during the colder seasons, which is why testing should be done in both hot and cold seasons.
Radon levels increase and decrease through a 24-hour "diurnal" cycle, climbing overnight while the house is closed up and dropping in the afternoon.
The EPA recommends mitigation at 4.0 pCi/L, but the majority of radon-related lung cancers come from homes measuring below 4.0 pCi/L. This is why we aim for ALARA: As Low As Reasonably Achievable.
The EPA’s action level of 4.0 pCi/L is not a safety threshold. It was set in 1986 based on what testing and mitigation could reliably achieve over forty years ago.
Radon is heavier than air and concentrates on lower levels — HVAC and ceiling fans can circulate it through the whole house.
The EPA's "potential elevated radon" maps can be misleading. They're based on decades-old data and don't reflect newer testing results. Radon has been found in every state and county in the U.S.
The Sierra Nevada mountains and foothills have many areas of naturally elevated radon, driven by our geology.
Children and pets may be more vulnerable. They have smaller lungs, breathe faster, and spend more time on the floor and the lowest level of a home, where radon is usually highest. A 2020 veterinary study found more lung tumors in dogs and cats living in high-radon areas.