Radon Health Risk Guide · EPA Data
Is Radon Dangerous? Health Risks Explained
Yes — radon is the second-leading cause of lung cancer in the US after smoking, responsible for approximately 21,000 deaths annually per EPA data. Iowa has the highest indoor radon in the nation (8.5 pCi/L average). Complete guide to risks, exposure effects, and safe levels.
What makes radon dangerous?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil. It is chemically inert — meaning it doesn't react with other substances in your body — but it is radioactive. When you breathe in radon, the gas itself is mostly exhaled before causing harm. The danger comes from radon's decay products, called "radon daughters" or "radon progeny": polonium-218, polonium-214, lead-214, and bismuth-214.
These solid radioactive particles attach to dust and aerosols, get inhaled, and lodge in the bronchial passages and lung tissue. As they continue to decay inside your lungs, they emit alpha radiation — a form of radiation that deposits high energy in a very small volume of tissue. This concentrated radiation damages the DNA in the cells lining the lungs. Over years of chronic exposure, this DNA damage can accumulate and eventually cause lung cancer.
Three things make radon especially dangerous:
- You cannot detect it. Radon is colorless, odorless, and tasteless. There are no acute symptoms. The only way to know your home's radon level is to test.
- It accumulates in homes. Radon enters through cracks and openings in foundations and concentrates in basements and lower levels. Indoor levels can be 10x or more higher than outdoor air.
- The damage is cumulative. A single high reading isn't the danger — it's years of chronic exposure that drives cancer risk. The longer you wait to test and mitigate, the more cumulative damage.
Radon Lung Cancer Risk by Level (EPA Data)
EPA risk estimates based on lifetime exposure (1 in N people will develop lung cancer at this radon level).
| Radon Level (pCi/L) | Non-Smoker Risk | Smoker Risk | EPA Recommendation |
|---|---|---|---|
| 20 pCi/L (very high) | 36 in 1,000 | 260 in 1,000 | Mitigate immediately |
| 10 pCi/L (common Iowa basement) | 18 in 1,000 | 150 in 1,000 | Mitigate immediately |
| 8.5 pCi/L (Iowa avg) | 15 in 1,000 | 130 in 1,000 | Mitigate |
| 4 pCi/L (EPA action level) | 7 in 1,000 | 62 in 1,000 | Mitigate |
| 2 pCi/L (EPA "consider") | 4 in 1,000 | 32 in 1,000 | Consider mitigation |
| 1.3 pCi/L (US avg) | 2 in 1,000 | 20 in 1,000 | Low priority |
| 0.4 pCi/L (outdoor avg) | <1 in 1,000 | ~3 in 1,000 | Background level |
Why Iowa has the highest radon-related risk in the US
Iowa\'s #1-in-the-nation indoor radon levels create proportionally elevated lung cancer risk per capita. Several factors converge:
- Geological: Uranium-rich glacial-till soils blanket most of Iowa, producing radon gas continuously. Eastern Iowa\'s Driftless Area adds fractured limestone bedrock that provides radon transport pathways.
- Housing stock: Most Iowa homes have full basements — the lowest level where radon concentrates. National housing stock with slab foundations (much of the South and West) doesn't accumulate radon as easily.
- Climate: Iowa winters drive the "stack effect" — heated indoor air rising creates negative pressure in basements that pulls radon-laden soil gas into the home. Winter readings are typically 30-50% higher than summer.
- Testing rates: Despite the #1 ranking, only ~25% of Iowa homes have been tested. Most elevated homes go unmitigated, perpetuating exposure.
- Smoking interaction: Iowa\'s smoking rate (~17% of adults) combined with high radon means the multiplicative smoker-radon risk affects a measurable share of the population.
The Iowa Cancer Consortium estimates that radon contributes to ~400 Iowa lung cancer deaths annually — a measurable share of Iowa\'s total lung cancer mortality. Iowa is one of the only states with an active state radon awareness program (Iowa HHS Radon Program, 515-281-4928) precisely because of the elevated statewide risk.
FAQ
Radon Health Risk FAQs
Frequently Asked Questions
Is radon actually dangerous to humans?
Yes. Radon is the second-leading cause of lung cancer in the United States after cigarette smoking, responsible for approximately 21,000 deaths annually according to EPA data. Radon is a naturally occurring radioactive gas; when inhaled, it decays into radioactive particles that lodge in lung tissue. Over years of chronic exposure, these particles damage DNA in lung cells and can cause lung cancer. The risk is proportional to both the radon level and the duration of exposure. Iowa, with the highest average indoor radon in the US at 8.5 pCi/L (more than double the EPA action level), faces disproportionate radon-related cancer risk per capita.
How does radon cause lung cancer?
Radon gas itself is chemically inert — the danger comes from its radioactive decay products. When radon is inhaled, it decays into other radioactive isotopes (polonium-218, polonium-214, lead-214, bismuth-214) called "radon daughters" or "radon progeny." These solid radioactive particles attach to dust and aerosols, get inhaled, and lodge in the bronchial passages and lung tissue. As they continue to decay, they emit alpha particles — a form of radiation that damages DNA in the cells lining the lungs. Over years of chronic exposure, this DNA damage accumulates and can lead to lung cancer. Alpha radiation is particularly damaging because it deposits high energy in a small volume of tissue.
What are the symptoms of radon exposure?
There are NO immediate or acute symptoms of radon exposure. This is what makes radon especially dangerous — you cannot see, smell, taste, or feel it, and there is no test a doctor can run to detect radon exposure short of lung cancer screening. The only symptoms are those of the lung cancer that develops years or decades after chronic exposure: persistent cough, shortness of breath, chest pain, recurring respiratory infections, hoarseness, coughing up blood, unexplained weight loss. By the time these symptoms appear, the cancer is typically advanced. This is why testing your home is the only way to know your radon level — it is impossible to detect through physical symptoms.
What is a safe level of radon?
EPA states that no level of radon exposure is completely safe — any radioactive exposure carries some cancer risk. However, the EPA action level is 4.0 pCi/L (picocuries per liter). The agency recommends mitigation for any indoor radon level at or above 4 pCi/L. Levels between 2-4 pCi/L are considered elevated, and EPA recommends "considering" mitigation. The WHO (World Health Organization) recommends a lower action level of 2.7 pCi/L. Iowa's average indoor radon is 8.5 pCi/L — more than double the EPA action level — meaning most Iowa homes exceed any safe threshold and would benefit from mitigation.
How much radon is too much?
EPA Action Level: 4.0 pCi/L (mitigation recommended above this). EPA Considering Level: 2.0-3.9 pCi/L (consider mitigation, especially with smokers or children in household). WHO Action Level: 2.7 pCi/L (more conservative than EPA). Iowa averages 8.5 pCi/L. The lifetime risk of lung cancer from chronic radon exposure at the EPA action level (4 pCi/L) for a non-smoker is approximately 7 in 1,000; for a smoker, the risk rises to 62 in 1,000 due to the multiplicative effect between smoking and radon. At Iowa's 8.5 pCi/L average, non-smoker risk approximately doubles. Higher levels (10+ pCi/L) common in Iowa basements significantly increase these risks.
Is short-term radon exposure dangerous?
Short-term radon exposure (days to weeks) at typical indoor levels is generally not dangerous. The cancer risk from radon comes from chronic exposure over years to decades. However, very high acute exposures (occupational levels of 100+ pCi/L for extended periods, historically seen in uranium miners) can cause more rapid lung damage. For residential exposure, the concern is chronic exposure — which is why a single elevated radon test result warrants mitigation even though you have not yet been harmed. Mitigation prevents future risk; it does not "fix" past exposure.
Is radon more dangerous for smokers?
Yes — significantly. Smoking and radon have a synergistic (multiplicative) effect on lung cancer risk rather than just additive. EPA data: at 4 pCi/L lifetime exposure, non-smoker lung cancer risk is ~7 in 1,000 over a lifetime. Smoker lung cancer risk at the same radon level is ~62 in 1,000 — roughly 9x higher. At higher radon levels common in Iowa (10+ pCi/L), the multiplied risk for smokers becomes substantially worse. EPA estimates that 90% of all radon-related lung cancer deaths occur in people who smoke or have smoked, even though smokers are not the majority of the population. For smokers, mitigation is particularly important.
Is radon more dangerous for children?
Children may face proportionally higher radon risk for several reasons: (1) Children breathe more rapidly than adults relative to body weight, inhaling more radon per unit time. (2) Children's developing lung tissue may be more susceptible to DNA damage. (3) Childhood radon exposure provides more years for cancer to develop. (4) Children spend significant time in basements (playrooms, family rooms) where radon concentrations are highest. EPA does not publish separate child-specific risk multipliers, but pediatric environmental health authorities recommend prioritizing radon mitigation in homes with children. Schools in Iowa are legally required to test for radon every 5 years for this reason.
Can radon affect pets?
Pets may face similar radon-related cancer risks as humans, though the research base is smaller. Cats and dogs that spend significant time in basements (the highest-radon areas of most homes) are exposed to the same elevated radon as humans in those spaces. Some veterinary oncologists believe radon may contribute to certain pet cancers, particularly in cats. The Iowa Cancer Consortium notes that pet radon exposure correlates with home radon levels, and mitigating for human safety naturally protects pets as well. Pet birds may be particularly vulnerable due to their efficient respiratory systems.
How long does radon stay in your body?
Radon gas itself does not accumulate in your body — its physical half-life is only 3.8 days, and gas inhaled is largely exhaled before it decays. The danger comes from radon decay products (radon "daughters" — polonium-218, polonium-214, lead-214, bismuth-214) that are inhaled and lodge in lung tissue. These solid particles can remain in lung tissue for varying periods, with some isotopes having half-lives of minutes (decay quickly) while others (lead-210) have a half-life of ~22 years and can persist in bone tissue. The cumulative DNA damage from chronic exposure is what drives cancer risk.
What states have the highest radon levels?
The top 10 states for highest average indoor radon (pCi/L): 1. Iowa (8.5), 2. Pennsylvania (7.5), 3. Ohio (6.0), 4. Kentucky (5.5), 5. South Dakota (5.0), 6. North Dakota (4.9), 7. Nebraska (4.8), 8. Minnesota (4.7), 9. Wisconsin (4.5), 10. Idaho (4.4). All of these states have widespread EPA Radon Zone 1 designation (highest risk). The "Midwestern radon belt" stretches from Iowa east through Ohio and includes much of the Plains states. Iowa's #1 ranking is driven by uranium-rich glacial-till soils, fractured limestone bedrock in eastern Iowa, basement-heavy housing stock, and cold-winter stack-effect intensification of radon entry.
What should I do if I have high radon levels?
Three-step response: (1) Verify the result — a single short-term test can sometimes show falsely elevated readings due to weather conditions or testing errors. EPA recommends a follow-up test, ideally a 90-day long-term test or a second short-term test, to confirm. (2) Mitigate — if confirmed above 4 pCi/L, install an active radon mitigation system through an NRPP-certified contractor. In Iowa this is also legally required to be done by an IDPH-licensed mitigator. Typical Iowa mitigation cost: $800-$2,500. (3) Re-test — 30 days after mitigation, conduct a verification test. Then re-test every 2 years to ensure continued system effectiveness.
Test Your Iowa Home for Radon
5 in 7 Iowa homes are above the EPA action level. Get a free testing or mitigation quote from an NRPP-certified Iowa partner contractor.