Radon Levels by State 2025

Radon is a naturally occurring radioactive gas that is odorless, tasteless, and colorless. The natural radioactive decay of uranium forms it in rock, soil, and water.

Radon is the second-leading cause of lung cancer, costing the United States over $2 billion per year in both direct and indirect healthcare costs. Radon has no immediate symptoms that will alert someone of its presence, and it takes years of exposure before any problems become apparent.

According to the US EPA, nearly 1 in 3 homes checked in seven states had radon levels over the recommended action level for radon exposure of 4 pCi/L. The pCi in “pCi/L” is a picocurie, which is one-trillionth of a curie and measures the rate of radioactive decay of radon. At 4 pCi/L, there will be approximately 12,672 disintegrations in one liter of air during a 24-hour period.

According to Air Chek, Inc., 31 states have radon exposure above 4 pCi/L. In general, these states are in the northern half of the United States. Only five states and the District of Columbia are considered to have low radon levels. Those states are:

• Arizona
• Florida
• District of Columbia
• Mississippi
• Louisiana
• Hawaii

Hawaii has the lowest radon levels of all 50 states, with an average level of 0 pCi/L. The uranium content of Hawaiian rocks is low, and most rocks near the surface are porous, allowing for air infiltration to dilute radon. Alaska has the highest radon levels of 10.7 pCi/L. Homeowners in Alaska are encouraged to test for radon every two years.