A naturally occurring radioactive gas, often released from soil and rocks. See also radon.

Above definition Copyright © The Home Ventilating Institute. Some content originally appeared in John Bower's book, Understanding Ventilation, published in 1995 by The Healthy House Institute.

From HousekeepingChannel.com:

Radon is a radioactive gas that is among the byproducts of the decay of uranium. This colorless, odorless gas also occurs naturally in almost all soil and rock, though concentration levels vary widely in different regions of the United States. Radon migrates through soil and can enter buildings and homes through foundation cracks or other openings, and through well water. Decay products of this gas can be inhaled into the lungs, where they continue to release radiation as decay continues. Exposure to radon can cause lung cancer.

According to the U.S. Environmental Protection Agency, high indoor radon levels are generally found in many counties of the inter-mountain West, northern and central Plains states, the central Midwest and along the Appalachians into New York state and New England. Counties with generally low radon concentrations are located in the piedmont region from Texas to the southeast Atlantic coast and Florida. However, the EPA recommends radon testing in all land-based conventional homes (but not in houseboats, etc.), regardless of location, since concentration levels can vary widely even within a community.

Many firms sell inexpensive testing kits that are placed in the home for a few days, and then sent back to the company for analysis. In many cases where radon concentration is elevated but not excessive, simple solutions, such as sealing foundation cracks and openings and adding powered or passive ventilation to a basement, are effective in reducing radon in the home. At hazardous levels, mitigation equipment installed by contractors may be necessary.