What Is Radon Gas and Why Should Homeowners Care?

Radon is a radioactive gas. You can't see it, smell it, or taste it. And it's the second leading cause of lung cancer in the United States, right behind smoking.

Where Does Radon Come From?

Uranium exists naturally in most soil and rock. As it breaks down, it produces radium. Radium decays into radon gas. That gas seeps upward through the ground and into the air.

Outdoors, radon disperses quickly and stays at harmless concentrations — around 0.4 pCi/L on average. The problem starts when it enters a building. Radon gets trapped indoors, accumulates, and reaches concentrations that pose real health risks over time.

It enters through cracks in foundation slabs, gaps around pipes, sump pits, crawlspace dirt floors, and even well water in some cases. Any home can have elevated radon. New construction, old construction, basement, no basement — none of that makes a home immune.

Why Is It Dangerous?

When you breathe in radon, its radioactive decay products (called progeny) lodge in your lung tissue. These particles emit alpha radiation that damages cell DNA over time. Enough damage, and cells can become cancerous.

The EPA and the National Academy of Sciences estimate radon causes roughly 21,000 lung cancer deaths annually in the U.S. The World Health Organization has also identified radon as a significant cancer risk and references a target level of about 100 Bq/m³ (approximately 2.7 pCi/L).

Here's what makes radon tricky: the risk is cumulative. It's not like carbon monoxide, where you get sick fast. Radon exposure builds over years and decades. By the time there's a diagnosis, the exposure happened long ago.

How Do You Know If Your Home Has It?

Testing. That's the only way. There are no symptoms of radon exposure that show up in time to prevent harm, and no visual clues in the home.

Short-term test kits (charcoal canisters or electret devices) sit in the lowest livable level of your home for 2 to 7 days. They give you a snapshot. Long-term tests (alpha track detectors) run for 90 days to a year and give a more accurate annual average.

You can also hire a certified radon measurement professional for a continuous monitor test, which logs hourly readings over 48 hours and is harder to tamper with — this is the standard for real estate transactions.

If your result comes back at or above 4.0 pCi/L, the EPA recommends taking action. But even between 2.0 and 4.0 pCi/L, the agency says you should consider mitigation. There is no known safe level of radon exposure.

What Do You Do If Levels Are High?

Mitigation. The most common approach is active soil depressurization — a contractor installs a pipe and fan system that pulls radon from under your foundation and vents it above the roofline. It's straightforward, effective, and typically costs between $800 and $2,500 for most homes.

A properly installed system can reduce radon levels by up to 99%. Post-mitigation testing confirms the system is working, and a simple U-tube manometer on the pipe lets you verify operation at a glance.

Common Misconceptions

A few things people get wrong about radon:

• "My neighbor tested low, so I'm fine." Radon levels can vary dramatically between adjacent homes. Soil conditions, foundation type, and air pressure dynamics are all hyper-local.
• "New homes don't have radon." Construction age has no bearing on radon levels. Some new homes test higher than older ones.
• "I don't have a basement, so I'm safe." Slab-on-grade homes and homes with crawlspaces can have elevated radon too. The gas enters through any contact point with the ground.
• "Opening windows fixes it." Ventilation can temporarily lower levels, but it's not a reliable long-term solution. Radon comes back as soon as the windows close.

The Bottom Line

Radon is a serious but solvable problem. Test your home. If levels are elevated, fix it. The testing is cheap, the mitigation is proven, and the health stakes are too high to ignore.

Use our radon risk lookup tool to check your area's risk level, or browse state and city pages to find certified radon professionals near you.