What is radon?

Radon is a radioactive gas released from the normal decay of the elements uranium, thorium, and radium in rocks and soil. It is an invisible, odorless, tasteless gas that seeps up through the ground and diffuses into the air. In a few areas, depending on local geology, radon dissolves into ground water and can be released into the air when the water is used. Radon gas usually exists at very low levels outdoors (about .5 pCi/L). However, in areas without adequate ventilation, radon can accumulate to levels that substantially increase the risk of lung cancer.

Everyone breathes in radon every day, but usually at very low levels. People who inhale high levels of radon are at an increased risk of developing lung cancer.  Radon can enter homes through cracks in floors, walls, or foundations. Less often, Radon is released from building materials or from water obtained from wells that contain radon. Radon levels are often higher in homes that are built on soil rich in the elements uranium, thorium, and radium. Basement and first floors typically have the highest radon levels because of their closeness to the ground.

How does radon cause cancer?

Radon decays quickly, giving off tiny radioactive particles. Outside, the body, the particles are not a problem because they are easily blocked by the skin.  When inhaled, however, these radioactive particles can damage lung tissue not protected by skin. Long-term exposure to radon can lead to lung cancer, the only cancer proven to be associated with inhaling radon.

How many people develop lung cancer because of exposure to radon?

Cigarette smoking is the most common cause of lung cancer. Radon represents a far smaller risk for this disease, but it is the second leading cause of lung cancer in the United States. Scientists estimate that 15,000 to 22,000 lung cancer deaths in the United States each year are related to radon.

Exposure to the combination of radon gas and cigarette smoke creates a greater risk of lung cancer than exposure to either factor alone. The majority of radon-related cancer deaths occur among smokers. However, it is estimated that more than 10 percent of radon-related cancer deaths occur among nonsmokers.

How can people know if they have an elevated level of radon in their homes?

Testing is the only way to know if a person’s home has elevated radon levels. Indoor radon levels are affected by the soil composition under and around the house, and the ease with which radon enters the house. Homes that are next door to each other can have different indoor radon levels, making a neighbor’s test result a poor predictor of radon risk.

The U.S. Environmental Protection Agency (EPA) recommends taking action to reduce radon in homes that have a radon level at or above 4 pCi/L of air. About 1 in 15 U.S. homes is estimated to have radon levels at or above this EPA action level. Scientists estimate that lung cancer deaths could be reduced by 2 to 4 percent, or about 5,000 deaths, by lowering radon levels in homes exceeding the EPA’s action level.

The EPA web site has more information about radon exposure.