Radon
Radon is a naturally occurring radioactive gas that can enter buildings from soil and rock, creating an indoor air risk that can only be known by testing.
What radon is
Radon is a naturally occurring radioactive gas. It forms as uranium, thorium, and radium break down in rocks, soil, and sometimes groundwater. Radon has no color, smell, or taste, so people cannot sense it without a test. Outdoors it usually disperses, but indoors it can accumulate.
How radon enters buildings
Radon commonly moves from soil into buildings through cracks, gaps, drains, crawl spaces, sump openings, construction joints, and other pathways in the foundation. Air pressure differences between the building and the soil can draw radon inward. Well water can also release radon indoors in some cases.
Why it affects health
When radon decays, it produces radioactive particles that can be inhaled and lodge in the lungs. These particles release ionizing radiation that can damage lung tissue over time. Radon risk is strongly linked to lung cancer, and exposure combined with smoking creates a much higher risk than either factor alone.
Testing homes
Radon levels can vary from house to house, even in the same neighborhood, so maps cannot replace testing. Short-term tests measure levels over a few days, while long-term tests give a better picture of average exposure across seasons. Testing is often recommended in the lowest lived-in level of a home.
Understanding results
Radon is commonly reported in picocuries per liter in the United States. The EPA action level is 4 pCi/L, meaning mitigation is recommended at or above that level. Lower levels can still carry some risk, so many public health messages encourage reducing radon as much as reasonably possible.
Mitigation systems
Radon mitigation usually focuses on preventing soil gas from entering the building or venting it safely outdoors. A common approach is active sub-slab depressurization, where a pipe and fan draw radon from beneath the foundation and exhaust it above the roofline. Systems should be installed and checked by qualified professionals when needed.
Schools, workplaces, and water
Radon is often discussed in homes, but schools, childcare centers, workplaces, and other buildings can also need testing. In areas where private wells draw from radon-rich geology, water may be tested too. The right response depends on local geology, building design, water source, and measured levels.
Why it matters
Radon matters because it is invisible, common, and preventable. A home can look clean and still have elevated radon. Testing and mitigation turn an unknowable indoor air hazard into a measurable and manageable risk, especially for households already concerned about lung health.