Historical, experimental and clinical evidence is presented to suggest that radon constitutes a relatively small carcinogenic risk for casual visitors to caves. The risk is dependent on radon levels and the smoking of tobacco. Show cave guides, chronically exposed to radon, may be at increased risk for lung cancer due to the effects of radon, especially if they are smokers of tobacco.
Craven, Stephen A. and Berend J. Smit.
Radon in caves: clinical aspects.
International Journal of Speleology,
Available at: http://scholarcommons.usf.edu/ijs/vol35/iss2/5