A review of recent studies confirms that some people are exposed to radon in their homes, and this puts them at risk for lung cancer. In fact, radon is the second leading cause of lung cancer after cigarette smoking.

Radon gas cannot be seen, smelled, or tasted. It occurs naturally when radioactive uranium decays. This is why states with high levels of uranium in their soil have the highest indoor levels of radon gas.

Radon levels are highest in mid-Atlantic states and the upper Midwest, and lowest in the Southeast to west Texas and much of the West coast.

The basement is where radon levels are highest in the home, because it is the closest room to the soil.

The latest review of radon exposure was reported in CA, A Cancer Journal for Clinicians (Vol. 51, No. 6: 337-344) by Howard Frumkin, MD, PhD, Rollins School of Public Health at Emory University, and Jonathan M. Samet, MD, Bloomberg School of Public Health, Johns Hopkins Medical Institutions.

The US Environmental Protection Agency (EPA) estimates that about 8 million US homes have unsafe radon levels.

In the 1950s and 1960s studies confirmed the link between radon exposure in mines and lung cancer. Studies to learn if radon in homes causes lung cancer began about 20 years ago, the authors said.

Scientists studied the levels of radon in current homes and in previous homes when possible, and compared this to records of people who did or did not develop lung cancer. They found higher radon levels increase the risk of developing lung cancer.

The authors noted that cigarette smoking and radon combined increase the risk of lung cancer more than each factor alone. Although all smokers should quit, smoking is especially dangerous to people with high radon levels in their homes.

According to Frumkin, "Radon in homes is an important public health issue."

"It contributes to a substantial number of lung cancer cases, especially among smokers," he said. "And very importantly, it is a hazard that can be readily detected, and often managed at low cost."

Radon exposure in homes can be tested easily. Homeowners can buy radon test kits in hardware stores or hire a company with experience in checking radon levels. Testing should be done more than once to average the results.

A variety of methods can be used to reduce radon levels in the home. Cracks in the floors and walls can be sealed, and pipes and fans can be installed. State radon offices can offer more information on correcting this problem. The EPA Web site also provides information on how to lower radon levels in homes.

The authors noted that about one-third of radon-induced lung cancer could be avoided if homes with radon exceeding 4 pCi/L (the EPA action level) could be corrected.