Radon is a naturally occurring, radioactive gas that forms when uranium in soil and rock breaks down. It is colorless, odorless, and tasteless, so it cannot be detected without testing equipment. Radon is dangerous because prolonged exposure to elevated levels is the leading cause of lung cancer among non-smokers and the second-leading cause overall, according to the EPA.
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What is Radon Gas?
Radon gas comes from the natural decay of uranium found in nearly all soil. As uranium breaks down, it releases radon, which rises through the ground and seeps into buildings through foundation cracks, sump pits, and gaps around pipes.
Radon exists outdoors too, but it disperses harmlessly in open air. The danger comes from radon accumulating indoors, where concentrations build up in basements and lower levels that have less air exchange with the outside.
Wisconsin’s soil and bedrock, much of it derived from granite and carbonate rock, is associated with a higher potential for elevated indoor radon than the national average, according to geologic analysis from the Wisconsin Geological and Natural History Survey and the Wisconsin Department of Health Services. That’s true across the whole state, not just certain suburbs, which is why testing matters for every home in the Milwaukee area, including in Whitefish Bay, Wauwatosa, West Allis, and South Milwaukee, regardless of the home’s age or foundation type.
How Is Radon Measured?
Radon is measured in picocuries per liter of air, abbreviated pCi/L. This unit reflects the rate of radioactive decay occurring in a given volume of air.
The EPA has set 4.0 pCi/L as the action level, the point at which homeowners should take steps to reduce radon exposure. The World Health Organization recommends a more conservative reference level of 2.7 pCi/L (100 Bq/m³), and says countries should aim for that level where possible.
No level of radon exposure is completely risk-free. Risk increases with both concentration and duration of exposure, which is why testing matters even in homes that come in below 4.0 pCi/L.
Why Is Radon Dangerous?
Radon is classified as a Group A human carcinogen by the EPA, placing it in the same risk category as asbestos and secondhand smoke. When inhaled, radon decays into radioactive particles that lodge in lung tissue and emit alpha radiation, damaging cells and DNA over time.
That cellular damage accumulates with prolonged exposure and can eventually lead to lung cancer. The EPA estimates radon exposure causes about 21,000 lung cancer deaths in the United States each year.
Key risk factors include:
- Duration of exposure — years of exposure in a home with elevated radon compounds the risk
- Concentration level — higher pCi/L readings mean faster cellular damage
- Smoking status — smokers exposed to radon face a dramatically higher combined risk than either factor alone
For a deeper look at the biological mechanisms, see our explanation of how radon affects your health.
How Does Radon Get Into a Home?
Radon enters buildings mainly through the foundation, following the path of least resistance created by pressure differences between soil gas and the home’s interior.
Common entry points include:
- Cracks in concrete slabs and foundation walls
- Gaps around pipes, sump pumps, and utility penetrations
- Exposed dirt floors in crawl spaces
- Block wall cavities and construction joints
Homes with well water can also introduce radon through faucets and showerheads, though soil gas infiltration is the dominant pathway. For a closer look at the sources, read our guide to where radon comes from.
How Common Is Radon in Homes?
Radon isn’t rare. The EPA’s national survey data puts elevated radon levels, meaning at or above the 4.0 pCi/L action level, in roughly one in every 15 homes nationwide, and it shows up in new construction and century-old homes alike, since the gas comes from the ground, not the building materials. Basements and lower levels are the most common trouble spot because they sit closest to the soil, but radon can migrate to upper floors too, especially in homes with poor air sealing between levels. We cover this in more detail in our article on why some homes have higher radon concentrations than others.
Radon levels also aren’t constant. They shift with barometric pressure, soil moisture, and season, which is one reason our article on how rain affects radon levels is worth a read if your test result seems inconsistent with a neighbour’s. For the full picture on radon’s properties and behaviour, see our complete guide to understanding radon: essential facts and safety.
What Are the Symptoms of Radon Exposure?
Radon exposure produces no immediate symptoms. There’s no headache, cough, or physical sensation that signals elevated radon in real time, which is why testing is the only reliable way to detect it.
Long-term exposure symptoms typically only appear as radon-induced lung cancer develops, often decades after initial exposure. That latency is exactly why the EPA and state radon programs urge every home to be tested regardless of how occupants feel. For a full breakdown, read our article on symptoms of radon exposure.
How Do You Test for Radon?
Radon testing uses either short-term or long-term devices placed in the lowest livable level of a home.
| Test type | Duration | Best for |
| Short-term | 2 to 7 days | A quick snapshot, useful for real estate transactions |
| Long-term | 90 days to a year | A more accurate average, since radon fluctuates with weather and season |
Testing should follow ANSI/AARST protocols to ensure accurate, defensible results. Homeowners in Whitefish Bay, Wauwatosa, West Allis, and South Milwaukee can review our full process in what radon testing involves and why it matters.
How Do You Fix a Radon Problem?
The most effective and widely used solution is sub-slab depressurization. A pipe is inserted through the foundation slab and connected to a radon fan that draws radon gas from beneath the home and vents it safely above the roofline.
Sub-slab depressurization typically reduces indoor radon levels by 80 to 99%, according to peer-reviewed field studies. Other mitigation methods include sealing foundation cracks, sump pit covers, and crawl space encapsulation, though these are usually supplements to active depressurization rather than replacements for it.
Mitigation should always be performed by a contractor certified through the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB). An improperly installed system can fail to lower radon levels or create new pressure imbalances in the home.
Frequently Asked Questions
Is radon dangerous at any level?
Radon risk exists at any concentration, though it increases with higher pCi/L readings and longer exposure. The EPA action level of 4.0 pCi/L is the threshold for recommended mitigation, not a safety cutoff.
Can radon be in any home, new or old?
Yes. Radon comes from soil, not building materials or age. New construction, older homes, homes with basements, and homes with crawl spaces can all have elevated radon.
How often should I test my home for radon?
The EPA recommends testing every two years, and immediately after any major foundation work, renovation, or HVAC changes that could alter airflow.
Does opening windows reduce radon?
Temporarily, yes, but this is not a permanent fix. Radon returns to prior levels once windows close. Only a certified mitigation system provides lasting reduction.
Is radon only a basement problem?
Basements typically show the highest concentrations since they sit closest to the soil, but radon can migrate to upper floors, especially in homes with poor air sealing between levels.
Conclusion
Radon is not a dramatic threat that announces itself. It is quiet, persistent, and dangerous precisely because it goes unnoticed. Understanding what radon is and why it matters empowers homeowners to take control of their indoor air quality.
Testing is simple. Mitigation is effective. The risk is real, but it is also manageable with the right knowledge and professional support. By addressing radon proactively, you protect your health, your home, and your peace of mind.
If you live in Whitefish Bay, Wauwatosa, West Allis, South Milwaukee, or anywhere else in the Milwaukee area, Milwaukee Radon Mitigation provides certified radon testing and mitigation system installation. Call 414-455-7279 to schedule a test or consultation.
