Radon is a colorless, odorless, tasteless radioactive gas. When radon gas is inhaled, the radioactive particles remain in the lungs. As radon gas decays further, it releases additional radioactive particles that can adhere to dust, which is also easily inhaled. Radon is the number one cause of lung cancer in non-smokers and the second leading cause of lung cancer (after tobacco) in smokers.
Radon is a naturally occurring byproduct of the decay of thorium and uranium. Radon is found in high concentrations in igneous rocks, such as granite. This is why Minnesota, situated on the granite-rich Canadian Shield, has higher levels of radon.