Radon

What radon is

Radon is a naturally occurring radioactive gas. It forms when uranium in soil, rock, and water breaks down over time, and that breakdown happens beneath the ground all over the country.

The gas itself is invisible and odorless, which is what makes it so easy to overlook. As radon decays, it releases tiny radioactive particles. When you breathe those particles in, they lodge in the lining of your lungs and give off small bursts of radiation that damage the cells over time. The EPA describes radon as the largest source of radiation exposure for most people, larger than any medical scan or industrial source they encounter in daily life.

Where radon comes from

Radon starts in the ground under and around your home. Uranium is common in soil and rock, so nearly every property sits on some amount of it, and the gas it produces is always working its way toward the surface.

The amount varies widely from one place to the next. Local geology decides how much uranium sits below a property, so radon levels can differ sharply between neighboring homes on the same street. The EPA divides the country into three radon zones based on predicted indoor levels, and it estimates that about 1 in 15 homes nationwide has a radon level high enough to warrant action. Well water can add to the load in some homes, releasing dissolved radon into the air during showers and washing, though soil remains the main source for most households.

How radon gets into your home

Radon moves from the soil into your home through the path of least resistance. The air pressure inside a house is usually a little lower than the pressure in the soil beneath it, and that difference pulls the gas upward through any opening it can find.

The entry points are the ordinary gaps in a foundation. Cracks in concrete slabs and basement walls, gaps around pipes and drains, sump pits, crawl spaces, and the joints where the floor meets the wall all let radon seep in. Once inside, the gas collects in the lowest levels first, which is why basements and ground floors typically show the highest readings. A tightly sealed, energy-efficient home can trap radon longer, because less fresh air moves through to dilute it. This is why two homes with similar soil beneath them can still test very differently depending on how they are built and sealed.

What radon does to your health

Radon damages the lungs, and it does so quietly over many years. When you breathe in its radioactive particles, they settle in lung tissue and release radiation that harms the cells lining your airways, and repeated damage of this kind is what can lead to cancer.

The scale of the risk is well documented. The EPA links radon to about 21,000 lung cancer deaths each year in the United States, and the Surgeon General has identified it as the second leading cause of lung cancer overall. The CDC reports that radon and smoking together raise the danger far more than either does alone, so a smoker living in a high-radon home carries a much greater risk than the numbers for radon by itself suggest. Radon causes no symptoms while it does its damage. There is no cough, no irritation, no warning sign, which means the exposure adds up silently until lung cancer appears years or even decades later.

Anyone can be exposed to radon, since it comes from the ground rather than from a habit or a product. The risk depends mostly on how high the level is in your home and how long you breathe it.

Smokers and former smokers face the steepest danger. The EPA notes that the combination of radon exposure and cigarette smoke multiplies the risk of lung cancer well beyond what radon causes on its own. People who spend long hours in basements or ground-floor rooms take in more, since those are the spaces where radon concentrates. Children may be more sensitive because they breathe faster and their lungs are still developing, though the clearest and best-measured risk across all groups comes down to the level in the home and the years of exposure it represents.

What a household can do

Test first, because testing is the only way to know your level and it costs almost nothing. Short-term radon test kits run about $15 at a hardware store or online, and many state radon programs offer them free or at a discount. You place the kit in the lowest lived-in level of your home, leave it for the recommended number of days, and mail it to a lab for results.

Act on the number the test gives you. The EPA recommends fixing your home if the radon level reaches 4 picocuries per liter or higher, and it suggests considering action between 2 and 4. If your level runs high, a radon mitigation system solves the problem reliably. The most common approach, called sub-slab depressurization, uses a pipe and a quiet fan to vent radon from beneath the foundation to the outside before it can enter the house. A professional system typically costs between $800 and $2,500 to install, the EPA reports, and it can lower radon levels by up to 99%. Retest every few years and after any major renovation, since changes to your foundation or ventilation can shift the level over time.