Why Is Radon Gas In Homes Considered A Problem?

Radon is a radioactive gas that forms naturally from the decay of uranium in soil and rock. You cannot see it, smell it, or taste it. It seeps into homes through cracks in foundations, gaps around pipes, and other openings, and it can build up to levels that raise the risk of lung cancer over years of exposure.

Radon is considered a problem because it is the leading cause of lung cancer among people who have never smoked, and the second leading cause overall after smoking itself. The U.S. Environmental Protection Agency estimates that radon exposure is responsible for thousands of lung cancer deaths each year in the United States. Because the gas is invisible and exposure produces no immediate symptoms, many people live with elevated levels without knowing it.

Why Is Radon Gas In Homes Considered A Problem?

Radon is dangerous because it emits ionizing radiation as it decays. When you breathe in radon particles, they can become trapped in the lining of your lungs. There, they continue to decay and release small bursts of radiation that can damage lung tissue at the cellular level. Over many years, this damage can lead to lung cancer.

The risk is not from a single exposure. It comes from long-term, continuous breathing of elevated radon levels inside a home. The higher the concentration and the longer the exposure, the greater the risk. This is why radon is measured in picocuries per liter (pCi/L) — a unit of radioactive concentration in air.

What makes radon especially concerning is how common it is. The EPA estimates that about 1 in 15 homes in the United States has elevated radon levels. That means roughly 7 million homes. Radon can be found in every state, in older homes and new construction alike, in basements and upper floors.

How Does Radon Get Into Your Home?

Radon forms underground when uranium, radium, and thorium decay in soil, rock, and water. As a gas, it moves upward through the soil and enters buildings through any opening that touches the ground.

Common entry points include:

• Cracks in solid floors and walls
• Construction joints where walls meet floors
• Gaps around service pipes, sump pumps, and drains
• Cavities inside walls
• Well water, especially from deep wells drilled into radon-rich rock

The amount of radon that enters a home depends on several factors: the concentration of uranium in the underlying soil, soil permeability, the home’s construction, and pressure differences between the soil and the indoor air. Homes can draw radon in through a process called the stack effect — warm indoor air rises and escapes through the upper floors, creating a slight vacuum at the foundation that pulls soil gas inside.

Two neighboring houses can have very different radon levels. You cannot predict your home’s level based on its age, style, or whether it has a basement. Testing is the only way to know.

What Radon Level Is Considered Dangerous?

The EPA sets an action level of 4 pCi/L. At or above this level, the agency recommends taking steps to reduce radon in your home. The World Health Organization recommends a lower reference level of 100 becquerels per cubic meter, which is roughly equivalent to 2.7 pCi/L.

There is no known safe level of radon. Even at 2 pCi/L, some risk exists, though it is lower than at 4 pCi/L. The action level is not a boundary between safe and unsafe — it is a practical threshold where the EPA believes the benefits of reduction clearly justify the cost.

Radon levels in a home fluctuate. They can vary by season, weather, and time of day. A single short-term test gives a snapshot. Long-term tests, which run for more than 90 days, provide a better picture of average exposure.

How Does Radon Cause Lung Cancer?

When radon gas is inhaled, it decays into solid radioactive particles called radon progeny. These particles can attach to dust, smoke, or other airborne particles and be breathed deep into the lungs. Once lodged in the lung lining, they continue to emit alpha particles — a type of radiation that, while unable to penetrate the skin, can damage cells when released in close proximity.

The alpha radiation can damage DNA in lung cells. If that damage is not repaired correctly, it can lead to mutations that accumulate over time and eventually produce cancer. This process typically takes many years. Radon-related lung cancer generally appears after decades of exposure, not months or years.

The risk is much higher for smokers. Radon and smoking together multiply the risk far beyond what either would cause alone. For people who have never smoked, radon is still the leading cause of lung cancer, but the absolute risk is lower than for smokers.

What Are the Symptoms of Radon Exposure?

There are no immediate symptoms of radon exposure. You cannot feel it, and it does not cause headaches, fatigue, or respiratory irritation in the short term. Symptoms, when they appear, are symptoms of lung cancer — a persistent cough, shortness of breath, chest pain, coughing up blood, or unexplained weight loss. These typically appear only after years of exposure and are not specific to radon.

This lack of warning signs is a key reason radon is considered a problem. There is no way to know you are being exposed without testing. By the time symptoms appear, exposure has usually been ongoing for a long time.

How Do You Test for Radon?

Testing is simple and inexpensive. You can buy a do-it-yourself radon test kit from hardware stores, online retailers, or your state radon program. Some states offer free or discounted kits. Professional testers are also available if you prefer.

Short-term tests take two to seven days. For a short-term test, you should keep windows and doors closed as much as possible during the testing period, though normal entry and exit is fine. Long-term tests run for more than 90 days and give a more accurate annual average.

If your short-term result is 4 pCi/L or higher, the EPA recommends a follow-up test — either a second short-term test or a long-term test — before making a decision about mitigation. If the average of two short-term tests is 4 pCi/L or higher, or if a long-term test is 4 pCi/L or higher, the EPA recommends fixing the home.

How Do You Reduce Radon in a Home?

Radon reduction, also called mitigation, is a well-established process. The most common method is sub-slab depressurization. A pipe is installed through the foundation floor and connected to a fan that pulls radon from beneath the home and vents it safely above the roofline. This prevents soil gas from entering the home in the first place.

Other methods include:

• Sub-membrane depressurization for crawl spaces
• Drain tile depressurization
• Block wall depressurization for homes with hollow-block foundations
• Sealing cracks and openings (usually as a supplement, not a stand-alone fix)
• Increasing ventilation or using heat recovery ventilators

Mitigation systems typically cost between $800 and $2,500, though costs vary by home and region. A properly installed system can reduce radon levels to below 2 pCi/L in many cases. The EPA recommends using a certified or licensed radon mitigation contractor. Many states have certification requirements, though not all do.

New homes can be built with radon-resistant features. These include a gas-permeable layer under the foundation, plastic sheeting, a vent pipe, and sealing of foundation openings. If radon levels are still elevated after construction, a fan can be added to the existing passive system.

Does Radon in Water Matter?

Radon can dissolve in groundwater, especially from private wells drilled into rock with high uranium content. When that water is used for showering, washing, or other household activities, radon can be released into the air. However, the EPA notes that radon in water generally contributes a much smaller portion of indoor radon than soil gas — typically about 1 to 2 percent of the indoor air concentration for homes with public water supplies.

For homes with private wells, the contribution can be higher. If your water comes from a well and your indoor radon levels are elevated, testing the water may be warranted. Point-of-entry treatment systems using granular activated carbon or aeration can remove radon from water. The EPA recommends treating water only when radon in water is a significant contributor to indoor air levels.

What About Radon in Schools and Workplaces?

Radon can accumulate in any building that contacts the ground, including schools, offices, and other workplaces. The EPA recommends that schools test for radon and fix problems when levels are at or above 4 pCi/L. Some states require testing in schools, but requirements vary. If you work in a ground-floor or basement space, radon could be present, though your employer may not have tested for it.

How Common Is Radon-Related Lung Cancer?

The EPA estimates that radon causes about 21,000 lung cancer deaths each year in the United States. Of those, roughly 2,900 occur in people who have never smoked. These figures are estimates, not exact counts, but they reflect the scale of the public health concern.

Lung cancer is the leading cause of cancer death in the United States for both men and women. Radon is the second leading cause of lung cancer overall, after smoking. For never-smokers, it is the leading cause. The evidence for this relationship comes from studies of underground miners exposed to high radon levels, as well as from residential studies in the general population. Both lines of research point in the same direction.