Radon is a naturally occurring gas you cannot see or smell, and it is the second leading cause of lung cancer after smoking. The good news: every home can be tested cheaply, and almost any home can be fixed. Radon 101 turns the official guidance into plain English so you know exactly what to do.
No fear-mongering and no jargon, just clear answers and the specific next step, backed by the agencies that set the standards.
What radon is, how it gets into a home, whether it is actually dangerous, and how worried you should really be.
Browse guides →How to test, short-term vs long-term kits, what a good test costs, and how to read your result against the EPA and WHO levels.
Browse guides →How a sub-slab depressurization system actually works, what mitigation costs, and where DIY makes sense versus hiring a pro.
Browse guides →Radon in real estate: testing during a sale, whether to buy a house that already has a system, and who pays for the fix.
Browse guides →The real health risk, the action levels explained, and why radon varies so much from one home and region to the next.
Browse guides →Recently published. See all guides →
Basements collect more radon than any other part of a home because they sit closest to the soil source and ventilate the least, making testing essential.
Read the guide →The EPA's radon zone map shows which US counties and states face the highest average indoor radon levels, and why your specific home can still surprise you.
Read the guide →Radon levels are shaped by soil geology, foundation type, and indoor pressure. Here is what pushes levels high and why two neighboring homes can read so differently.
Read the guide →Iowa, North Dakota, Pennsylvania, and a cluster of Midwest states top every radon survey. Here is what the EPA data shows and what to do about it.
Read the guide →The U.S. EPA sets the 4 pCi/L action level that all 50 states follow, but average radon concentrations and state programs vary considerably by region.
Read the guide →The EPA's 4 pCi/L action level is not a safety cutoff. Here is what the number actually means, how it was set, and what to do if your home exceeds it.
Read the guide →This is your home, your health, and your money, so we do not guess. We translate the authorities, the U.S. EPA, Health Canada, the WHO, and the radon-professional bodies (AARST-NRPP and C-NRPP), into clear, practical guidance, and we tell you when a step is worth it and when it is not. We are an independent publication, not a testing or mitigation company, so we have no reason to talk you into anything.
You cannot fix what you have not measured, and a test kit is the cheapest insurance there is.
See our picks and learn how to read the result.
See the best radon test kitsQuick, plain-English answers to the questions homeowners ask most. This is educational guidance, not medical advice.
Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in soil and rock. You cannot see, smell, or taste it, and it can seep into a home through the foundation and build up indoors. It matters because the U.S. EPA and the World Health Organization identify radon as the second leading cause of lung cancer after smoking. The reassuring part is that radon is easy to measure and almost any home can be fixed.
Radon is measured in picocuries per liter (pCi/L) in the United States. The U.S. EPA sets an action level of 4 pCi/L, meaning the EPA recommends taking steps to lower radon if your long-term average is at or above that figure. The EPA also notes that some risk remains at lower levels and you may wish to consider reducing radon between roughly 2 and 4 pCi/L. There is no level of radon that is considered completely free of risk, so lower is always better. For Canadian readers, Health Canada uses a different unit and guideline, so always check the standard that applies where you live.
The most common approach is a do-it-yourself test kit, which you place in the lowest lived-in level of your home according to the instructions and then send to a lab for analysis. You can also hire a certified radon professional to perform the measurement. Because radon levels change with weather, season, and how the home is used, follow the kit directions carefully and keep windows and doors closed as instructed during a short-term test.
A short-term test usually runs from a couple of days up to about 90 days and gives you a quick snapshot, which is useful when you need an answer fast, such as during a home sale. A long-term test runs for more than 90 days and better reflects your year-round average because it captures seasonal swings. The EPA generally suggests confirming an elevated short-term result with a follow-up test before deciding on mitigation.
The most common fix is an active sub-slab depressurization system, which uses a fan and a vent pipe to draw radon from beneath the foundation and release it safely above the roofline before it enters your living space. Cost is driven by factors such as your foundation type, the size and layout of the home, how the pipe must be routed, and local labor rates. A certified radon professional can assess your specific home and recommend the right system.
When buying, you can ask whether the home has been tested and request a radon test as part of the inspection, often using a short-term test because of the tight timeline. A home that already has a mitigation system is not a red flag, since it means the issue was identified and addressed. When selling, having a recent test or an installed system can give buyers confidence. Who pays for a test or a fix is negotiable and varies by local custom, so discuss it with your real estate professional.
No. Radon 101 is an independent educational publication, not a testing or mitigation company and not a medical provider. We translate guidance from authorities such as the U.S. EPA, Health Canada, and the World Health Organization into plain English, but nothing here is medical advice or a substitute for professional radon testing or mitigation. For decisions about your home and health, follow those authorities, a certified radon professional, and your local guidelines.