Radon Exposure: What Homeowners Need to Know
Radon is invisible, odorless, and tasteless, which is exactly what makes it dangerous. You cannot see it seeping up through the basement floor or smell it in the air you breathe at night. Radon exposure builds quietly over years, and the only way to know whether it is happening in your home is to test. Colorado sits in a high-radon zone, so this is a practical concern for Front Range households, not an abstract one. This guide summarizes EPA and CDC guidance current as of 2026 for general education; it is not a medical diagnosis, and questions about your health should go to a physician.
What Is Radon Exposure?
Radon exposure means breathing air that contains elevated levels of radon gas over time. Radon is a naturally occurring radioactive gas produced when uranium in soil and rock breaks down. It rises from the ground and can accumulate inside buildings, where it becomes concentrated enough to pose a health risk. The EPA sets the action level at 4 picocuries per liter (4 pCi/L), meaning a confirmed indoor reading at or above that number is the point at which it recommends fixing the home.
Exposure is cumulative. A single hour in a high-radon room is not the concern; years of breathing elevated air is. That is why the EPA frames radon risk in terms of long-term average concentration rather than a single moment, and why testing measures levels over days or months rather than minutes.
How Does Radon Exposure Happen?
Radon moves from soil into homes through the path of least resistance. Indoor air is often at slightly lower pressure than the soil beneath a foundation, especially in winter when warm air rising in a house creates a gentle vacuum that pulls soil gas inward. The gas enters through cracks in slabs and walls, gaps around pipes, sump pits, crawl spaces, and porous block foundations.
Because the lowest levels of a home are closest to the soil, basements and ground-floor rooms typically show the highest concentrations. Well water drawn from radon-bearing rock can also release the gas indoors when the water is agitated during showering or dishwashing, though soil gas is the dominant source in most homes. The geology of the Colorado Front Range, with uranium-bearing rock and soils, is a key reason the region reports so many elevated readings.
Who Is Most at Risk?
Everyone who breathes elevated indoor radon faces some added risk, but the EPA and CDC note that the danger is far greater for people who smoke. The combination of smoking and radon exposure multiplies lung-cancer risk well beyond either factor alone. Children are sometimes raised as a concern because of their developing lungs and longer remaining lifespan of exposure, though the strongest evidence base concerns adult lifetime exposure.
What Are the Health Effects of Radon Exposure?
The principal health concern is lung cancer. When radon decays, it produces tiny radioactive particles that can lodge in lung tissue and damage cells over time. According to the EPA, radon is the second leading cause of lung cancer in the United States after smoking, and the leading cause among people who have never smoked. The American Lung Association describes radon as responsible for thousands of lung-cancer deaths each year.
Radon exposure does not cause immediate symptoms. There is no cough, headache, or rash that signals a high level, which is part of why testing matters so much. The risk is statistical and long-term, accumulating over years of breathing elevated air. Anyone concerned about lung-cancer risk or respiratory symptoms should speak with a physician rather than attempting to interpret exposure on their own. For a closer look at the biological mechanism, our companion guide on what radon does to you explains how the decay particles affect the lungs.
How Do You Reduce Radon Exposure?
The first step is always testing. Short-term test kits give a quick snapshot over two to seven days, while long-term tests measure for 90 days or more and better reflect true average exposure. The EPA recommends confirming any elevated short-term result before acting. The full radon testing process for Front Range homeowners walks through which test fits which situation.
If a confirmed level reaches or exceeds 4 pCi/L, the proven fix is an active mitigation system that vents soil gas above the roofline before it enters living space. These systems reliably bring levels well below the action threshold. Our overview of the way a radon mitigation system works details the components and what installation involves. Sealing cracks helps marginally but is not a standalone solution, and the EPA is explicit on that point.
How Often Should You Test?
The EPA recommends testing every home, retesting every two years, and testing again after any major renovation or change to the heating and ventilation system. Real-estate transactions are another natural trigger, since many Colorado buyers request a radon test as part of due diligence. Retesting after a mitigation system is installed confirms the exposure has actually been reduced.
How Is Radon Exposure Measured?
Radon exposure is expressed in picocuries per liter of air (pCi/L), a unit that counts radioactive decay events rather than a physical volume of gas. The EPA action level of 4 pCi/L is the threshold at which it recommends fixing a home, though it notes that no level is entirely free of risk and that homeowners may choose to act between 2 and 4 pCi/L. In other parts of the world, levels are reported in becquerels per cubic meter, but in the United States picocuries per liter is the standard.
Because exposure is cumulative, the average concentration over time matters more than any single reading. A long-term test that runs 90 days or more gives a better estimate of true annual exposure than a two-day snapshot, which can be skewed by weather, season, or whether the house was closed up. Radon levels also tend to run higher in winter, when homes are sealed and the stack effect pulls more soil gas indoors, so the testing season influences the result.
Where Exposure Is Highest in a Home
Concentrations are usually greatest in the lowest occupied level because that space is closest to the soil source. A finished basement used as a bedroom or home office can therefore deliver more exposure than an upstairs room, simply because of how much time is spent there and how close it sits to the foundation. The EPA recommends testing in the lowest livable level for this reason, and placing the test where people actually spend time.
How Long Does Radon Exposure Take to Cause Harm?
There is no instant injury from radon. The risk accumulates over years of breathing elevated air, which is why the health concern is framed as a long-term, statistical increase in lung-cancer risk rather than an acute illness. The EPA models lifetime risk based on the average concentration and the number of years of exposure, and the relationship is roughly proportional: higher levels and longer exposure both increase risk.
This long timeline is precisely what makes radon dangerous to ignore. Because nothing feels wrong, families can live for a decade or more in a high-radon home without any prompt to act. A child raised in such a home accumulates exposure across their developmental years, and an adult who works from a basement office adds hours of daily exposure. Reducing the level at any point lowers the ongoing risk, so it is never too late to test and mitigate.
Radon Exposure From Water
Soil gas is the dominant source in most homes, but radon can also enter through well water drawn from radon-bearing rock. When that water is agitated, during showering, running a faucet, or operating a dishwasher, dissolved radon is released into the indoor air. Public water systems that use surface water generally pose little risk, but private wells in geologically active areas can contribute.
The contribution from water is usually smaller than from soil, and the EPA notes that the air pathway is the primary concern for most households. Still, homeowners on private wells in high-radon regions may want to test their water as well as their air. If water-borne radon is significant, treatment systems such as aeration or granular activated carbon can reduce it at the point of entry.
What Reduces Radon Exposure Most Effectively?
The proven, durable solution is an active mitigation system, which the EPA identifies as the most reliable way to lower indoor radon. Improving ventilation, sealing cracks, and increasing air exchange can each help marginally, but none reliably brings a high level below the action threshold on its own. Sealing in particular is useful only as a supplement that makes a fan-driven system more efficient.
For households where someone smokes, reducing radon is especially urgent because the two risks multiply. Quitting smoking and lowering radon together produce a far greater risk reduction than either alone. After any mitigation, a follow-up test confirms the exposure actually dropped, and the EPA recommends ongoing retesting every two years to ensure the reduction holds over time. Colorado’s high-radon geology makes this routine vigilance worthwhile across the Front Range.
Why Colorado Sees So Much Radon Exposure
The Front Range sits on geology that practically manufactures radon. Uranium-bearing rock and soils are common across the region, and as that uranium decays it produces a steady supply of radon gas that migrates upward through permeable soil toward the surface. Combine that source with the way homes are built and operated, and elevated indoor levels become common rather than rare. The Colorado Department of Public Health and Environment reports that a large share of homes tested statewide come back above the action level.
Cold winters compound the effect. When a home is sealed against the cold and the heating system runs, the stack effect intensifies, drawing more soil gas indoors through foundation cracks and openings. Basements, which are common in Front Range homes and often finished into living space, sit closest to the soil source and tend to show the highest readings. The result is a region where testing is not a precaution for the unlucky few but a sensible step for nearly every household.
New Homes Are Not Exempt
A frequent misconception is that newer construction is safe. In practice, tightly sealed modern homes can concentrate radon more than older, draftier ones because there is less natural air exchange to dilute it. Some new Front Range homes include passive radon-resistant features, but those do not guarantee a low level and should still be confirmed with a test after move-in. Age of the home tells you little; only a measurement tells you the actual exposure.
Steps to Lower Your Family’s Exposure Today
The practical sequence is straightforward and worth restating. First, test the lowest livable level of the home, using a long-term kit when possible for a more accurate average. Second, confirm any elevated short-term result with a follow-up test before spending on mitigation. Third, if the confirmed level reaches or exceeds 4 pCi/L, install an active mitigation system through a certified contractor and verify the reduction with a post-installation test.
Beyond the system, supporting habits help. Keep the mitigation fan running continuously, glance at its manometer periodically, and retest every two years and after major renovations. For households where someone smokes, reducing both radon and tobacco exposure delivers the largest combined risk reduction. These steps are within reach of any homeowner, and they turn an invisible, accumulating risk into a managed one. Given the region’s geology, treating radon testing as routine home maintenance is the most sensible posture a Front Range family can take.
Key Points to Remember About Radon Exposure
Radon exposure is the cumulative result of breathing elevated indoor air over years, and its principal danger is an increased risk of lung cancer. The EPA action level of 4 pCi/L marks where fixing a home is recommended, though no level is entirely free of risk. Because radon is invisible and produces no symptoms, testing is the only way to know your exposure, and Colorado’s geology makes elevated levels common across the Front Range.
The response is well established and within any homeowner’s reach: test the lowest livable level, confirm an elevated reading, and install an active mitigation system if the confirmed level meets or exceeds the action threshold. Retest every two years and after major renovations, and for smokers, reduce both radon and tobacco for the largest combined risk reduction. Turning an invisible, accumulating hazard into a measured and managed one is straightforward once you commit to testing.
References
- Health Risk of Radon — U.S. Environmental Protection Agency
- About Radon — Centers for Disease Control and Prevention
- Radon — American Lung Association
Front Range homeowners who want to measure their actual exposure and talk through results with a qualified professional can get connected to a vetted local inspector through our contact page.