Radon at Home: Why Testing Matters and How to Fix High Levels
Table of Contents
Knowing more about radon
This guide is for general information; follow local authorities and qualified professionals for site-specific hazards.
The air in a home feels ordinary – quiet, familiar, easy to ignore. That’s exactly why radon slips past notice. You can’t see or smell this naturally occurring radioactive gas, and yet it can accumulate indoors to levels that raise a family’s lifetime risk of lung cancer. Whether you live over a crawlspace, a slab, or in a basement apartment, the only way to know your home’s radon level is to test. Fortunately, the remediation process for radon is well understood and effective [1].
Radon is a radioactive gas that forms naturally from uranium in soil and rock. When it seeps through slabs and foundation joints, it can build up indoors. Radon exposure is the second leading cause of lung cancer in the United States – posing risk for both smokers and non-smokers. Public health agencies recommend testing every home and acting promptly if results are elevated [2][3].
What is radon?
Radon (Rn 222) is a radioactive noble gas produced by the decay of naturally-occurring radioactive elements, such as trace amounts of uranium found in the soil. Radon moves from the ground into buildings through cracks and gaps in slabs and foundations. Due to its high molecular weight, radon is the heaviest known gas and tends to accumulate at the lowest levels of enclosed spaces, such as in basements and crawl spaces. As radon decays, it forms radioactive isotopes of the elements just below it on the periodic table – particularly polonium (Po-218), lead (Pb-214) and bismuth (Bi-214) [11]. These decay byproducts, known as radon daughters, are solid particles that can become attached to dust particles in the environment – especially in low-lying, unventilated spaces such as basements. When disturbed, these radioactive dust particles become airborne and are subsequently be inhaled into the lungs – exposing the inhaler to a radioactive dose and over time, increasing the risk of lung cancer and other health concerns.
Environmental testing is the only way to detect an elevated presence of radon in a building or enclosed space, since this gas is otherwise colorless, odorless, and causes delayed health impacts after a long period of exposure [1].
How Does Radon Impact Health?
While radon itself is a non-reactive noble gas, it rapidly decays into radioactive solid particles that can become attached to ambient dust and inhaled. Over a long period of exposure – such as from an undetected buildup of these particles in a home – radon byproducts can damage lung tissue and substantially increase the risk of lung cancer. Radon exposure is the second-leading cause of lung cancer behind tobacco smoking, and the leading cause of lung cancer among non-smokers [2]. Additionally, radon exposure has a synergistic effect with the damage to the lungs caused by tobacco smoke – exposure to both of these risk factors greatly increases the risk of developing lung cancer. The National Cancer Institute attributes 15,000 to 22,000 deaths per year in the US to the long-term health impacts of indoor radon exposure [5].
While radon is present at low levels throughout the environment, it decays after a few days and its radioactive byproducts disperse in outdoor environments before they have the chance to accumulate. Exposure becomes a health risk in low-lying, enclosed, unventilated spaces such as basements, where these elements can accumulate to hazardous levels over time and cling to dust and surfaces. Radon gas is colorless and odorless, and exposure to its radioactive byproducts does not produce immediate symptoms. This is why testing is needed to detect the presence of this silent killer in indoor spaces!
Where is Radon Risk Highest?
Due to radon originating from natural uranium in soil and rock, the risk of radon infiltration into homes varies based on region-specific geology. The U.S. Geological Survey’s geologic radon potential maps combine soil, rock, and radioactivity data to estimate where elevated indoor levels are more likely, helping programs target outreach and building practices [6]. EPA’s Map of Radon Zones similarly identifies areas with higher potential based on measurements and geologic factors [7].
Radon potential is highest in the northern half of the United States – in regions such as the Midwest and Great Plains, as well as the Rocky and Appalachian mountains. Colorado is an example of a state where radon risk is elevated across geologic regions, with nearly half of tested homes in the state exceeding the EPA’s action level of 4 pCi/L. State and local guidance works to educate residents on how radon can penetrate indoor spaces through cracks, utility openings, and pressure differences, and how to test for and remediate these issues [8].
How to test for radon
Testing for radon in a home or other indoor setting can be done through either a short-term or a long-term testing method. Short-term tests are the quickest and cheapest way to check a home – testing kits can be picked up at a hardware store for around $15-20. Short-term tests collect data on radon levels for 3-7 days, and are suitable for initial testing, as well as assessing radon levels after a home renovation or the installation of a radon mitigation system [11]. Long-term tests collect similar data over a period of 90 days or longer, and provide a more accurate view of the average radon levels in an indoor space, since short-term measurements can be influenced by weather conditions, occupancy patterns, and other transient environmental factors. Radon testing devices should be placed on the lowest lived-in level, away from drafts, high humidity areas, and exterior walls. Both testing types are easy to use and passively acquire data through environmental sampling. If you have questions about what type of testing you should use, a state radon office can help you choose the right device for your situation [5].
The EPA’s standard for radon intervention is 4 pCi/L, although levels between 2 and 4 pCi/L can still be reduced to further lower risk. Start testing with a short-term test – if the result is 4 pCi/L or higher, follow up with either an additional short-term test for a quick result, or a long-term test for a better average. Multiple data points are important for assessing the situation, especially when using short-term tests, because environmental factors such as home renovations and changes in ventilation, weather, and occupancy can impact short-term test results [1]. If multiple tests show a consistently elevated radon level of above 4 pCi/L, it is time to take action!
How Does Radon Mitigation Work?
Consistently elevated radon levels in a home or indoor spaces require professional remediation. Although we here at Air Support Project recommend DIY solutions, such as improvements to ventilation or the installing portable or handmade air purifiers in an indoor space, as a short-term fix for a lot of indoor air quality issues, that advice doesn’t apply here. HEPA filters do not filter radon gas out of the environment, and while these units can remove some of the particulate byproducts created by radon decay, doing so risks contaminating the unit itself with radioactive lead and polonium isotopes.
Lowering elevated radon levels requires addressing the problem at its source – which typically involves structural issues present in the building that allow naturally-occurring radon to infiltrate the space from the soil. The most common method that contractors use is known as active sub-slab depressurization – in which suction point is created beneath the building’s foundation, and a fan and pipe system is used to vent the soil gas outdoors. This system maintains a slight vacuum below the living space to prevent radon from entering the living space. Sealing points of entry in basements and crawlspaces is an additional step that is often taken to reduce radon infiltration.When installed by a qualified professional, these systems reliably reduce indoor radon, often substantially below the action level [1].
After installation, follow-up testing confirms if the remediation system is working effectively, and if any adjustments are needed. Because radon risk has no true “safe” threshold, many families aim to reduce as much as practical given their home’s design. Regular home testing, maintenance, and re-testing after renovations can help ensure that mitigation systems are working properly and ensure a safe living environment over the long-term [3].
Advice for Renters
If you rent, ask whether the building has been tested and request a copy of results. In federally insured or assisted multifamily housing, HUD policy sets expectations for radon assessment, testing, and mitigation in line with national standards. This includes routinely testing ground-floor and basement units, mitigating buildings at or above 4 pCi/L, and verifying the effectiveness of the remediation with follow-up testing. These requirements apply across key multifamily programs and are intended to protect residents during refinancing, rehabilitation, and new construction [10].
Small Actions, Durable Protection
At Air Support Project, we believe everyone should know the steps they can take and tools they can use to keep their home safe from airborne contaminants – including radon.. Testing for radon is an easy and inexpensive process – a $20 kit from the hardware store can give you information on your home’s risk within a week. Although mitigating elevated radon levels is a more intensive process – often requiring professional remediation – the tools for doing so are well-established and can protect you and your family from devastating long-term health consequences. Radon is a solvable indoor air problem, and knowing what you can do to address this problem goes a long way to ensuring a safer, healthier future.
“When you can measure what you are speaking about, and express it in numbers, you know something about it.”
- U.S. Environmental Protection Agency. “A Citizen’s Guide to Radon.” EPA, Dec. 2016. https://www.epa.gov/sites/production/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf.
- U.S. Environmental Protection Agency. “Health Risk of Radon.” EPA, last updated 27 Feb. 2025. https://www.epa.gov/radon/health-risk-radon.
- Centers for Disease Control and Prevention. “Radon and Your Health.” CDC, 16 Feb. 2024. https://www.cdc.gov/radon/about/index.html.
- World Health Organization. WHO Handbook on Indoor Radon: A Public Health Perspective. 2009. https://www.who.int/publications/i/item/9789241547673.
- National Cancer Institute. “Radon and Cancer.” NCI, reviewed 6 Dec. 2011. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/radon/radon-fact-sheet.
- U.S. Geological Survey. “Geologic Radon Potential Map of the United States.” USGS. https://www.usgs.gov/data/geologic-radon-potential-map-united-states.
- U.S. Environmental Protection Agency. “The EPA Map of Radon Zones.” EPA, last updated 2 Dec. 2024. https://www.epa.gov/radon/epa-map-radon-zones.
- Colorado Department of Public Health & Environment. “Understanding Radon.” CDPHE. https://cdphe.colorado.gov/hm/understanding-radon.
- National Radon Program Services (Kansas State University). “U.S. Surgeon General Issues New National Health Advisory on Radon.” https://sosradon.org/radon-advisory-story.
- U.S. Department of Housing and Urban Development. “Guidelines for Radon Testing and Mitigation in HUD Owned or Assisted Multifamily Housing (Notice H 2013-03).” HUD, 31 Jan. 2013.
https://www.hud.gov/sites/documents/13-03hsgn.pdf. Wikipedia. “Uranium Decay Chain – Graphic”. - American Lung Association. “Radon Testing Kit Store” https://action.lung.org/site/Ecommerce?store_id=34304.
Melissa Smallwood
Melissa Smallwood is Science and Technology Policy researcher with a background in neuroscience, psychology, and social science, and the author of The Future of Long COVID: A Threatcasting Approach. They are interested in how disability and healthcare justice intersect with emerging technologies, and are an advocate for COVID mitigation strategies to help end the pandemic.
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