Radon gas comes from the natural breakdown of the traces of uranium in soil, rock and water.  There are no symptoms from radon exposure.  You cannot see radon, smell it, or even taste it. It is the second leading cause of lung cancer, estimated to cause around 23,000 lung cancer deaths annually in the United States.  The only lung cancer cause more dangerous than radon radiation is smoking.

This estimate from the National Academy Of Science indicates that around 1 in every 10 lunch cancer deaths may be caused by radon gas each year and that radon is 7th leading cause of all cancer.

You cannot estimate radon levels by neighborhood, home age, home design (on slab, crawl space or basement), energy efficiency, or even what the home next door reads.  Getting a radon test is the only way to know for sure!