Radon gas is radioactive, meaning it breaks down into subatomic bits called alpha particles that release small bursts of energy. When these particles strike the nucleus of cells in the lining of the lung, they damage the DNA, the genetic material that regulates the life and growth of cells. Over a long period of time, this cumulative damage can lead to lung cancer. It may take up to 25 years for lung cancer to develop. Not everyone who breathes radon gas will develop lung cancer. Smoking also damages lung tissue. So a person who smokes and is exposed to radon gas is at a much higher risk for developing lung cancer.

Radon is a radioactive gas. It's produced by the natural breakdown of uranium, which may be in rocks, soil, or water. Radon is an odorless, colorless gas that can seep into buildings through holes and cracks in the foundation. Radon is found all over the U.S., but in varying quantities. Nearly 1 in every 15 homes may have a radon problem, the EPA says. Radon levels are most critical at homes (versus at work or school) because that's where people spend most of their time.

When radon gas seeps into a home, the structure traps the gas inside, where it builds up. Radon can seep into both old and new homes, homes that are well sealed and homes that are drafty, and homes with or without basements, the EPA says. The only way to know if you have a radon problem is to have your home tested for radon.

Radon levels can be checked with a radon detection device that is left in the home for 2 to 90 days. These devices can be bought at a hardware or home improvement store. If the test shows that your home level exceeds 4 pCi/L, you should test your home again. You can use the 2-to-90-day test. Or you can use a long-term test called an alpha track detector. This measures radon levels for 3 months to a year. Private radon testers also can do the testing for you. The EPA advises taking action to reduce radon in homes that have a radon level at or above 4 pCi/L. Nearly 1 in 15 U.S. homes is estimated to have radon levels at or above this level.

Well water can be from a private well or from a public supply that relies on groundwater. Radon in water poses 2 problems: Drinking it and inhaling the gas released when the water is used for showering and other purposes, the EPA says. The health risk for inhaling radon is much greater than the health risk for drinking radon-contaminated water. Public water systems may treat the groundwater to reduce the amount of radon it contains. Private well water can be treated by removing the radon as it enters your home. You can also make sure your bathroom, laundry room, and kitchen are well ventilated.

Several methods are used to reduce the amount of radon in the home. Sealing the cracks in floors and walls may help. A soil suction system uses pipes and fans to suck the radon from below the foundation or in the crawl space before it enters the home. A radon contractor can help you decide which method is best for your home. A system installed when a house is being built usually is much less expensive. Ask if a house has been tested for radon before buying it or moving in.