--- title: What Is Radon and Where Does It Come From? canonical: "https://radonmitigationyorkpa.net/radon-guide/what-is-radon/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "Radon is a colorless, odorless radioactive gas made as uranium in soil and rock breaks down. Learn where it comes from and why homes trap it." --- # What Is Radon and Where Does It Come From? Radon is a colorless, odorless radioactive gas. It forms naturally when uranium in soil and rock breaks down into radium and then into radon. The gas rises through the ground and can build up inside homes, especially in basements and lower floors. You can't see, smell or taste it, so testing is the only way to find it. Our page on [radon levels and geology in York County](/york-county-radon-levels/) shows how this plays out here. ## Radon in plain English Radon is a natural gas, like the oxygen and nitrogen in the air you breathe. The difference is that radon is radioactive. Its atoms are unstable, and they break down over time, giving off small bursts of energy as they do. Radon is also a "noble gas." That means it doesn't react with other chemicals. It doesn't burn, it doesn't stick to things and it doesn't combine with other substances. It simply drifts wherever air carries it. You can't detect it with your senses. There is no smell, no color and no taste. Smoke detectors and carbon monoxide alarms don't sense it either. A radon test is the only way to know how much is in your home. ## Where radon comes from Radon starts with uranium, a natural element found in small amounts in nearly all soil and rock. Uranium has been in the earth since the planet formed. It breaks down very slowly, through a chain of steps: 1. **Uranium** slowly breaks down into other elements. 2. One of those is **radium**, which is also radioactive. 3. Radium breaks down into **radon gas**. 4. Radon then breaks down into tiny radioactive particles, often called radon decay products or progeny. The main form of radon that matters in homes, radon-222, has a half-life of about 3.8 days. That means half of it breaks down in under four days. But because the uranium and radium in the ground keep producing more, the supply never runs out. Some rocks and soils have more uranium than others. Granite, some shales, phosphate-rich rock and certain metamorphic rocks can be higher. Soils formed from weathered limestone can also hold more uranium and radium, as the U.S. Geological Survey has noted for parts of Pennsylvania. ## Why radon builds up indoors Outdoors, radon mixes with a huge volume of air and stays at low levels. EPA puts the average outdoor level at about 0.4 pCi/L. Inside, things are different. A house sits on top of the soil like a lid. Radon moving up through the ground can slip in through openings in the foundation and get trapped. Because air inside a home is usually at slightly lower pressure than the soil gas below, the house actually pulls radon in. If you want the details, here is [how radon gets into a house](/radon-guide/how-radon-enters-a-home/). EPA estimates the average U.S. home has about 1.3 pCi/L of radon. Many homes are far higher. EPA recommends fixing at 4.0 pCi/L or above. ## Radon in water Radon can also dissolve into groundwater. Homes on private wells can get radon from water, which is released into the air when you shower, wash dishes or run laundry. For most homes, soil gas is a much bigger source than water. But if you are on a well, it can be worth testing your water too, especially if your air results are high. ## Why radon matters for health The concern with radon is long-term exposure. When you breathe radon in, its decay products can lodge in your lungs. As they break down, they give off radiation that can damage lung cells. Over many years, that damage can lead to lung cancer. EPA estimates radon causes about 21,000 lung cancer deaths in the U.S. each year. It is the leading cause of lung cancer among people who have never smoked, and the second leading cause overall ([EPA radon information](https://www.epa.gov/radon)). Smoking and radon together raise risk much more than either alone. There are no immediate symptoms. Radon does not cause headaches, rashes or allergies. The risk builds silently over time. ## Radon in York County York County is in EPA Radon Zone 1, the highest-potential group. Its geology includes limestone in the York Valley, metamorphic rock such as schist and phyllite in the south, and shale, sandstone and diabase in the north ([DCNR geology of York County](https://maps.dcnr.pa.gov/publications/Default.aspx?id=61)). These rocks and their soils supply radon, and cracks and fractures give it easy paths to the surface. PA DEP's test data for the county shows about half of reported tests at or above 4.0 pCi/L. That makes radon one of the most common home issues York homeowners face, whether the house is a century-old row home or new construction. Pennsylvania takes radon seriously. Under state law, anyone who tests for or reduces radon in someone else's home must be certified by PA DEP ([PA DEP Radon Division](https://www.pa.gov/agencies/dep/programs-and-services/radiation-protection/radon-division)). ## Common myths about radon **"Only old houses have radon."** False. EPA says any home can have a radon problem: old or new, drafty or tight, with or without a basement. **"My neighbor tested low, so I'm fine."** Not necessarily. Two homes side by side can have very different results. **"I'd smell it or feel sick."** No. Radon has no smell and causes no immediate symptoms. **"Opening windows fixes it."** Fresh air can lower levels for a short time, but EPA treats natural ventilation as a temporary measure only. **"Radon is a scam to sell systems."** Radon is measured, studied and tracked by EPA, CDC, the World Health Organization and state agencies. The health risk is well documented. ## What you can do The good news is that radon is easy to test for and very fixable. - **Test.** Use a short-term test for a quick answer or a long-term test for a year-round picture. Test the lowest lived-in level. - **Compare to EPA guidance.** Fix at 4.0 pCi/L or higher. Consider fixing between 2 and 4. - **Fix with a proven method.** Active soil depressurization pulls radon from under the house and vents it above the roof. EPA calls sub-slab suction the most common and usually the most reliable method. - **Confirm the result.** A clearance test after installation shows whether the system worked. ## Key takeaways - Radon is a colorless, odorless, radioactive gas. - It forms naturally as uranium in soil and rock breaks down. - Homes trap radon and can pull it in through the foundation. - It is the leading cause of lung cancer among people who have never smoked, per EPA. - Testing is the only way to know your level, and high levels can be fixed. ## Frequently Asked Questions ### Is radon the same as carbon monoxide? No. Carbon monoxide comes from burning fuel and can cause sudden illness. Radon comes from the ground and causes no immediate symptoms. They need different detectors. ### Can radon come from building materials? It can in some cases, such as certain stone or concrete. But for nearly all homes, the soil under the house is the main source. ### Does radon stay in my belongings or clothes? No. Radon is a gas that does not stick to things. Once a home's air is cleaner, the radon is gone. ## See radon data for your area Want to know how common high radon is near you? Our York County radon levels page shows PA DEP test data by ZIP code, plus local geology. To test or fix your home, call [(717) 356-3035](tel:+17173563035) any time for a same-day callback.