Radon is a gas that is produced by the breakdown, or radioactive decay, of uranium naturally found in most earth materials.  It is a colorless, odorless, and tasteless gas that has been proven to be a large indoor air health threat, which can greatly increase the risk of lung cancer.

Radon Levels in the US.  Image Credit: EPA.

Large quantities of radon are found in many homes throughout the United States.  The substance can enter a building in a number of ways and can also be dangerous when present in drinking water.  When radon is inhaled, particles trapped in the lung continue to break down and release radiation that can damage lung tissue.  Prolonged exposure to this gas significantly increases the chances of developing lung cancer.  This danger increases as the duration of exposure increases and can be especially serious in the case of smokers.

The Environmental Protection Agency has done a number of studies on radon.  It has found the gas to be the second leading cause of lung cancer in the United States.  Other data has shown that long-term exposure to low levels of radon can actually be more damaging than short-term exposure to higher levels. 

Many comparisons have been made between the risk of lung cancer from smoking and that from radon.  For example, a slightly above-average level of radon can be equivalent, in terms of long-term effects, to smoking ten cigarettes a day or having 200 chest x-rays a year.  The highest recorded radon level was equivalent to smoking 200 packs of cigarettes a year.

The EPA on radon