Radon gas

Radon is a colorless and odourless gas generated by the breakdown of radioactive radium, which in turn is the decay product of uranium, found in the earth's crust. Radon exposure is the second major cause of lung cancer after smoking. The radiation ionizes genetic material, causing mutations that sometimes turn cancerous. Radon gas levels vary by locality and the composition of the underlying soil and rocks. For example, in areas such as Cornwall in the UK (which has granite as substrata), radon gas is a major problem, and buildings have to be force-ventilated with fans to lower radon gas concentrations. In the US, the EPA estimates that one in 15 homes has radon levels above the recommended standard.

Radon causes lung cancer because it causes arbitrary damage to the chromosomes and DNA molecules contained in the nucleus of the cell.