All rocks and soils contain some radium, so all rocks and soils give off some amount of radon. In buildings, radon concentrations can be much higher than outdoor levels. Click here to see more details. In a very small fraction of homes, drinking water can be a significant source of radon. Most such homes have private wells that draw water from particular geologic formations.
Radon is radioactive.
No serious scientist doubts that exposure to very high concentrations of radiation increases the risk of cancer. Additionally, there is evidence that radon is much more dangerous to smokers than to non-smokers. Click here to find out more about how we know radon is dangerous. . OK, so very high exposures are dangerous. For lower concentrations the data are less clear.