Health advocates are urging New Brunswickers to have their homes tested for a potentially dangerous and cancer-causing gas.

About 25 per cent of homes in the province have radon levels that exceed national guidelines, according to a two-year Health Canada study.

That's higher than anywhere else in the country, the study shows.

Radon exposure is the second-leading cause of lung cancer, after smoking, said Barb MacKinnon, of the New Brunswick Lung Association.

Radon is caused by the breakdown of uranium when soil degrades. It has no smell, taste or colour

"It's a gas that comes from the ground and it can accumulate in buildings, such as your home. And everyone needs to test their home for radon because if your home is over the Health Canada guideline of 200 becquerels per metre cubed, then you should have your home mitigated or something done to reduce the levels for radon," MacKinnon said.

Smoking and radon can increase risk

Radon tests cost about $40 and can be picked up at hardware stores or the Lung Association.

The device resembles a small hockey puck.

"You basically take it out of the plastic package, put it at chest level in a lived-in area of your basement and you basically just leave it there for a period of about three months," said Dr. Christin Muecke, the regional medical officer of health in Fredericton.

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The only known health impact of radon is increased risk of lung cancer, says Dr. Christin Muecke. (CBC)

The test is then mailed in a pre-addressed envelope to a laboratory for testing.

"Within about two weeks you get your results," said Muecke.

"Then you can decide to take action."

If high radon levels are detected, fixes can range from sealing cracks and holes in basements to higher cost options including installing systems to drain the gas off.

The only known health impact is increased risk of lung cancer, said Muecke.

That would generally occur over decades of exposure, she said.

"But if people are living in their home for a period of their lives and they have increased levels of radon in their home, it is possible it could increase their risk of lung cancer."

Muecke also said the combination of smoking and radon is "multiplicative."

"People who are smoking in homes with increased radon actually have much increased risk," Muecke said.