Understanding US Radon Levels by State: Is Your Home at Risk?

“There is no safe level of radon. Reducing radon inside your home or building will always help reduce your risk of lung cancer.”

– US Centers for Disease Control and Prevention (CDC)

Radon is the biggest source of natural-occurring radiation that people are exposed to everyday. It is colorless, odorless and tasteless, making it difficult to detect without proper testing. It accumulates in the air naturally through the breakdown of metals in the Earth's crust. Radon gas can seep into buildings, especially homes, and accumulate to potentially harmful levels.

Radon levels are measured in terms of pCi/L, which refers to picocuries per liter of gas. A picocurie is one trillionth of a curie, a unit of radioactivity. According to the US CDC, if your radon levels are above 4 pCi/L, you should take measures to reduce radon in your home.

When radon is released from the ground outdoors, it's easily diluted by the surrounding air. Outdoor radon levels typically vary between 0.135 to 0.405 pCi/L. The bigger concern arises when radon accumulates indoors.

Living in a basement with a radon level of 20 for a duration of five years poses an equivalent risk to living in a house with a radon level of 10 for a period twice as long. If you, or someone you know, are currently living in the basement, take proactive steps to check for harmful radon exposure.

The likelihood of lung cancer due to radon exposure depends on several factors:

• Radon concentration - The higher the radon concentration in a person's living environment, the greater the risk of lung cancer.
• Exposure duration - Prolonged exposure to elevated radon levels increases the risk. The longer someone is exposed to high radon concentrations, the higher the likelihood of developing lung cancer.
• Smoking status - Smokers are at a higher risk of developing lung cancer from radon exposure compared to non-smokers. Smoking and radon exposure have a synergistic effect, meaning their combined impact is greater than the sum of their individual effects.
• Overall health - Other factors such as pre-existing lung conditions and genetics can influence an individual's susceptibility to lung cancer.

Learn more: Radon-Induced Lung Cancer: The Silent Threat to Non-Smokers

In 2023, Alaska topped the chart by being the state with the highest average radon level (10.7 pCi/L) in the US. Other US states with the highest radon levels are:

Notably, it was recently found that over 70% of homes in Iowa have average radon levels above the Environment Protection Agency (EPA) threshold of 4 pCi/L. On average, the radon level in Iowa homes is 6.1 pCi/L.

In January 2025, the Iowa Department of Health and Human Services and the American Lung Association (ALA) started an initiative to provide free radon test kits in Iowa.

High levels of radon in Iowa may be attributed to the state’s glacial history. The passage of glaciers over Iowa led to the deposition of finely ground rocks that contain radium. The deposit constitutes a large surface area that emits radon gas.

If you reside in high radon areas, the EPA recommends to:

• 1. Test – Radon test kits are inexpensive and can be purchased online or from hardware stores. EPA recommends testing all homes below the third floor.

Long-term radon tests (for more than 90 days) are typically more reliable for determining a home's year-round average radon level as compared to short-term tests. This is because short-term tests (usually 2 to 7 days), may not accurately represent fluctuations in radon levels over time. Radon levels can vary due to factors like weather conditions, ventilation changes, and seasonal influences.

A radon test is the only way to know if radon is a problem in your home. It's simple and affordable, and may save your life.

• 2. Mitigate - If your radon levels are elevated, consider hiring a professional radon mitigation contractor to reduce radon concentrations in your home. They can install ventilation systems and other measures to lower radon exposure.

Based on the house dimensions, a radon mitigation system typically costs between $700 to $4000. However, the average homeowner will pay around $1000. This investment not only makes your home safer but also alleviates concerns about potential lung health issues.

• 3. Maintain – The mitigation system requires occasional maintenance, such as repairing or replacing parts and regularly checking the warning device. The EPA recommends retesting of home radon levels every two years.

If your home radon level is below 4 pCi/L, you can prevent radon accumulation by ensuring good air circulation in the house. This can be done by opening the windows and increasing air flow using fans or vents. However, these strategies only provide a temporary effect in maintaining low indoor radon levels.