People should test for the naturally occurring radioactive gas radon in their homes to help prevent ill health, the American Lung Association urges.

In some areas, like the state of Connecticut, radon was found to be present at high levels in a quarter (26%) of all homes.

Radon is emitted from the ground and can enter a house through floor cracks, basement walls and foundations.

Exposure to radon is the second-leading cause of lung cancer in the United States and it is the leading cause in people who've never smoked. It's responsible for an estimated 21,000 U.S. lung cancer deaths each year, the ALA said.

"Since radon is odorless, tasteless and colorless, the only way to detect radon in your home is to test the air," said Ruth Canovi, director of advocacy for the lung association.

"Radon Action Month is the perfect time to learn more about this dangerous gas and take action to protect yourself and your loved ones," Canovi said in an association news release.

The U.S. Environmental Protection Agency (EPA) sets an action level of 4 picoCuries per liter or pCi/L for radon.

Anyone with a radon level that high should have a professional install a mitigation system in their home, according to the EPA.

Both the EPA and the lung association recommend doing so if levels are greater than 2 pCi/L.

A radon mitigation system seals cracks and openings and includes a vent pipe and fan that collects radon gas from under the foundation and vents it outdoors.

Your state's radon program can provide a list of certified radon mitigation professionals.