"GENEVA -- The World Health Organisation (WHO) has drastically cut the maximum amount of radon -- a naturally occurring gas -- that should be permitted in homes because of strong evidence it causes lung cancer.

In a WHO Handbook on Indoor Radon issued on Monday, it called for public health authorities and the construction industry to make great reductions in exposure to radon, calling it a 'major and growing public health threat in homes.'

Radon is a cancer-causing radioactive gas that humans cannot see, smell or taste. It arises from the natural decay of uranium and can seep into homes through cracks in basements or cellars."

Stephanie Nebehay reports for Reuters September 22, 2009. [2]