Radon - The Silent Hazard

Exposure is preventable. Reliable testing kits are widely available and there are steps you can take to stop radon from concentrating at unhealthy levels in your home or business, usually by sealing cracks and increasing airflow.

Lauren Chambliss

May 7, 2021 • Updated May 10, 2023 • 5 min read
Natural Hazards
Find radon levels and other environmental hazards near you here


Radon is an invisible and odorless gas that comes from the natural breakdown of radium in rock and soil. Usually, it seeps through basements or foundations -- or the parts of buildings that touch the ground -- but it can also invade a home or business through water. It affects old and new buildings, single-family residences and large, public housing complexes. It's everywhere and, in concentrated forms, it's dangerous. Outside air has unharmful levels of radon but problems start when it builds up and concentrates inside spaces where airflow is weak.

In the 1970s, scientists established a clear link between radon and lung cancer. Since then, national and state regulatory agencies have adopted guidelines on acceptable levels, and many states require testing for radon upon the sale or transfer of homes. Some parts of the country have higher levels of naturally occurring radon than others, and even within states, the levels can vary. For example, in California, homes in Santa Barbara County have higher risk than those down the coast in San Diego County.

The Environmental Protection Agency (EPA) publishes risk information, from high-to-medium-to-low, for each state. Recent studies have found unacceptable levels in many homes, despite widespread publicity about its dangers. For example, in New York, state authorities say that in some counties, one-third to one-half of homes have levels over the recommended safety guidelines. Pennsylvania authorities found 65 percent of homes tested in one county had radon levels high enough that homeowners should take action to reduce them. Exposure is preventable. Reliable testing kits are widely available and there are steps you can take to stop radon from concentrating at unhealthy levels in your home or business, usually by sealing cracks and increasing airflow.

The US EPA’s radon exposure map displays three distinctly colored zones. Zone 1 is colored red and represents the highest radon potential. These counties have an average indoor radon level of 4 picocuries per liter. Zone 2 is colored orange for moderate potential, with average radon levels between 2 and 4 picocuries per liter. Zone 3, with the lowest risk of exposure, is yellow and has less than 2 picocuries per liter. The Midwest, Mountain West, Northeast and Mid-Atlantic appear to have the highest concentration of Zone 1 counties. The South is almost entirely in Zone 3. A level of 4 pCi/L or higher is considered hazardous. Even if radon levels are less than 4 pCi/L, they pose a risk, and in many cases they can be reduced, although below 2 pCi/L is difficult.

Buildings can be constructed to be resistant and many national health-advocacy groups, such as the American Lung Association, are pushing for stricter national and state guidelines to promote radon-safe construction codes.

Your Home and Radon#

Health and Safety#

Numerous studies have established that long-term exposure to radon gas can damage DNA, leading to genetic mutations that cause cancer. Radon attaches to tiny particles of indoor dust, which, when inhaled, stick to the lining of our lungs. Radon is believed to be the number one cause of lung cancer in non-smokers. According to the Centers for Disease Control (CDC), radon is responsible for about 20,000 cases of lung cancer annually. For smokers, the combination of tobacco and radon exposure is a toxic mix that greatly increases the chances of the most dreaded lung disease to 1-in-4.

While some reports have blamed radon for other illnesses, the link is less clear. Most experts believe that inhaled radon does not permeate beyond the lining of the lungs and is not likely to be responsible for other cancers in the body.

Exposure to radon, especially when combined with second-hand cigarette smoke, is particularly concerning for children and adolescents, who spend as many as 15 hours a day indoors. Children are considered more sensitive to the decay products of radon than adults, and prolonged childhood exposure likely increases the risk of lung cancer later in life.

Although some people have worried about radon escaping from granite or stone countertops, scientific experiments have essentially ruled out kitchen stonework as a significant source of radon. Most exposure comes from the basement or the lower levels in homes, which are closest to the soil.

Property Values#

Some states require radon tests as part of the sale of a home. The EPA says an unacceptable level is anything over 4/pCi/L, or four picocuries per liter. Though, the EPA recommends that people consider taking action at 2 pCi/L or above, since no exposure level is without risk. The average indoor level in the U.S. is 1.3 pCi/L, while outdoor levels average 0.4 pCi/L.

Because radon is prevalent throughout the country, it is not believed to impact home values generally, though if radon is found at concentrated levels in a particular home or building, it might scare off a buyer, even if radon-removing equipment is installed by the seller.

What You Can Do#

If you are buying a home, business or building, insist on a radon test, whether required by law or not. Test regularly to ensure levels are not building up in your basement or other closed, lower spaces where radon could leak in and concentrate. Testing kits are widely available in hardware stores and online, though it is a good idea to buy one that is registered, or recommended, by a state agency or other respected authority. Some local agencies offer them for free. Testing devices are usually placed in the lowest occupied level of the home or workplace.

Radon levels can vary from day-to-day and season-to-season so to get an accurate reading, you will need more than one test. If your radon score is high, meaning you live in an area with more risk, repeated testing is especially important. For instance, radon gas tends to be worse in wet months than dry.

Most home sales that provide radon information rely on inexpensive tests that provide a one-time snapshot of radon. It is good information, but if you have any concerns, consider long-term (greater than three months) testing. The more extensive testing will yield information on a home's average year-round radon levels. Long-term testing kits that monitor continuously are available, though they may need to be installed by a professional.

If your home has tested high for radon levels, or if you draw water from a private well, you should check your water, too. Public water that comes from a surface source, such as a lake or reservoir, is usually fine because radon disperses before it hits your tap. On the other hand, if your water comes from a well, especially in parts of the country with higher levels of radon in soil, testing is recommended. You can call the National Radon Program Services Hotline, 1-800-SOS-RADON, for your state radon office, which can direct you to water testing laboratories. Home testing kits are available, too. If you find high levels in your water, there are several things you can do, including carbon filtration and aeration.

Fortunately, there are two solutions to radon build-up:

  1. Create barriers to entry by sealing cracks and gaps or openings in the basement or below the slab of the home or building.
  2. Remove radon once it is inside by installing active ventilation.

AreaHub’s Knowledge Center is updated regularly and provides information drawing upon scientific studies and sources.

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