While any amount of exposure to radon gas constitutes a health risk, your
risks of contracting lung cancer decrease significantly as radon levels decrease. For example, a person living in a house with a radon level of 4.0 pCi/L or lower has an approximately 7 in 1000 chance of getting sick. On the other hand, a person living in a house with a radon level of 20 pCi/L or higher has a 36 in 1000 chance of contracting lung cancer. The World Health Organization (WHO) established an action level of 2.7 pCi/L based upon a three-year worldwide study by more than 30 prominent scientists.